USA passport holder....reentering the USA is by far the most painful process of any country I've ever visited, and I've been to quite a few places that aren't exactly best friends of the United States.

Oddly enough, I've been hassled the most entering from Canada - both out west in Washington and at various points east in Michigan, New York, or Vermont.

Immigration has only been an issue for us once in returning to the US--the one day we ended up with an inspector in the tourist lines. (The lines were extremely unbalanced, they routed a bunch of us citizens over to the other section.) He had a hard time with the concept we didn't bring back any souvenirs. (Hey, you have our travel record in front of you. Lots of trips to the same place. She has a foreign name and clearly learned English as an adult. Shouldn't it be obvious we were visiting her family, not really playing tourist??)

We do get lots of agricultural inspections but I wouldn't call that hassling.

My wife miscounted the number of blank pages in her US passport (she included the "amendments" page in her count) which resulted in both of us being escorted to the border police offices at JNB on arriving from MAD. The officials tried to trick her into offering a bribe (which would have been disastrous) and threatened to put us back on the Iberia plane, but eventually relented and let us into South Africa. Our bags were unmolested, still going round and round on the carousel.

The large group of Chinese people in the police office, part of a "Sino-Swazi Development Commission" evidently en route to Eswatini, were still there, probably lacking the required transit visas.

Hmmmm. For passport control / country entry only, two now come to mind:

YYZ (US immigration on flight home) - many years ago. "Where do you live?" "Richmond, California." "I didn't know any white people lived there."

YVR - many years ago (and before the electronic kiosks) - we were traveling with just a little backpack, and were on a sub-$200 RT from SFO. "Purpose of your trip?" "We're up here for lunch - for the day." Questioning continued until finally she asked "How much was your ticket?" I pulled the receipt out, showed her, and we were on our way.

I forgot about my recent YYZ US immigration experience. The woman in charge of managing the lines (e.g. moving ropes and directing traffic flow) was one of the most obnoxious border control people I've ever encountered. She barked orders at passengers, ignored pleas from poor souls who were in danger of missing connections, and was simply caustic. When someone mentioned to her (somewhat loudly) "we pay your salary, and you're not earning it," she replied that she was a contractor. I reported her to the officer, who stamped me through. He told me he passes on reports about her 5 times per shift (when they are both on duty at the same time).

Istanbul
My wife travels with a Malawian passport and was detained in Turkey because they didn't believe that "Republic of Malawi" was a real country. We spent about 15 minutes while supervisors were called, checked every page of her passport, asked some ridiculous questions ("if Malawi is in South Africa why don't you have a South Africa passport?"), googled Malawi and found it on a map, made some phonecalls and eventually took photographs of the passport to presumably show other immigration people that the country actually does exist! :D

Johannesburg (1)
Flew into South Africa many years ago with a colleague that held a Dominican Republic passport. SA immigration kept mixing it up with Dominica, the key difference being that Dominica required an advance visa while Dominican Republic did not. Took about 15 minutes and summoning of supervisors, plus reference to some thick book, before they eventually let us through.

Milan Malpensa
I happened to land at Malpensa very early in the new year for a day trip and was probably the immigration officer's first customer of 2005. Unfortunately, he had forgotten to roll his date stamp over from 2004 to 2005, something that neither of us noticed until later. When I was departing Malpensa later that day, I was stopped at departure immigration and accused of overstaying my entry permit. I was baffled since I had only arrived a few hours prior. The officer then showed me that the stamp was dated 2004 rather than 2005!! Thankfully, the officer with the outdated stamp was still on duty downstairs and someone was able to verify that he STILL hadn't rolled the stamp over to 2005. In addition, my passport had only been issued in August 2004 - so there was no way it could have been stamped in January 2004. I was sent on my way with a bunch of laughs.

Warsaw
Arriving into Warsaw from Amsterdam (pre Poland joining Schengen) in the evening, there was some fat slob in a ketchup-stained Stasi-surplus uniform standing at immigration and pulling aside anybody who had skin darker than his. I spent 45 minutes being grilled about my hotel accomodations by this guy (who suffered from severe halitosis) and his translator. Interesting observation - he would ask the question in Polish, the translator would repeat it in English and I'd respond in English - but the translator wouldn't repeat my response to him in Polish. Instead, he would simply move on to the next question. So he either understood English and my responses, or he simply didn't care. In the end, I was finally deemed acceptable to Poland and released together with a black American who had been similarly grilled. An Indonesian and a Bangladeshi were still being detained though.

Johannesburg (2)
Back when I was station manager for my airline at Johannesburg, when I received a panic call from the Captain who had just arrived asking me to come down to immigration. Evidently, they were insisting on seeing RETURN TICKETS for the CREW!!! He claimed that there was nowhere in his manual that exempted operating crewmembers from the requirement of holding a return air ticket. Did he think they were gonna disappear as illegal aliens and abandon our 767 parked outside??? Needless to say, a quick call to his supervisor had the crew released with apologies, but we wasted a good 10 minutes arguing over what was quite possibly the stupidest argument of all time.

Doha
I was visiting Doha as part of a diplomatic delegation invited by the Government of Qatar and my visa was supposed to have been sponsored by the relevant Qatari ministry. Unfortunately, I traveled seperately from the rest of my team (they flew EK and I flew in on QR) so the diplomatic "E-visa" was not filed properly in the system. So when I arrived in Doha at 5am or some other similar unearthly hour they couldn't find my visa and started processing me for deportation. I was taken off to the holding cells where the other undesirables (mainly migrant workers with fake permits) were being held, but fortunately I managed to reach our delegation leader on my mobile before I could be thrown into the cell. He woke up the relevant officials at the Ministry who sorted things out quickly and secured my release.

Luanda
Another official delegation, this time invited by the Government of Angola. Landed into Luanda and was immediately flagged as dodgy seeing that I had just arrived from Namibia traveling on an Indian passport holding an Angolan diplomatic visa issued in Pretoria stating that I represented the Government of Ghana. They tried to interrogate me in Portuguese but I couldn't understand a word they were saying. I finally managed to use my phrasebook to ask them to call the Embassy who could vouch for me, but they refused. Fortunately, the Embassy official assigned to pick me up from the airport had wondered where I had gotten to by now and wandered into the immigration area where he located me and sorted things out.

London Gatwick
When I was station manager for my airline at Gatwick, I wound up having to fly back-and-forth-and-back-and-forth from our head office daily for 5 consecutive days. About 4 days into this exercise, I was stopped by immigration at Gatwick who looked at my passport and saw multiple pages of entry/exit stamps with sequential days (LGW entry, destination entry, desination exit, LGW entry, destination entry, etc..). I tried to explain the reason but the lady wasn't buying it. "Are you trying to say that your job is to sit on this plane and fly back-and-forth all day long?". "Yes, yes exactly." "Right, go have a seat over there and someone will be with your shortly." She then went to the CIO who picked up the phone to call the airline station manager to verify the story. My mobile phone rang and I answered, telling him to have a look at me waving at him in the waiting area. That ended that pretty quickly and the CIO later became a friend of mine.

Passport control the only one that comes to mind is arriving on a cruise ship into Vancouver, Canada. Encountered a brand new immigration officer who was offended that I wasn't bringing anything for my friends in Canada (I did when I came in at the beginning of the cruise) and could not comprehend the fact that I'd met my travel companions through a cruise board similar to FT. After 20 minutes of that he finally let me go, only for my travelmate to step up and get the same inquisition.

Most interesting customs experiences were entering and exiting Ghana with medical supplies while on a medical missions trip. I saw some very interesting parts of ACC.

One of my most fun customs experiences was returning to the US from Colombia on a medical missions trip. "Returning from Colombia, any drugs in those bags?" "Yes officer those 4 big bags right there." "Have a nice day."

So, the countries to avoid/preapre for in advance are US, Canada and NZ?

This was pre-kiosk but I didn't have a great experience with US border control at YYZ. Early in the morning, directed to the immigration guy... stood at the counter for a good five minutes before the border agent acknowledged me. Was gruff and apparently annoyed that I was waiting to get processed to be on my way. Asked me the usual questions (in a "I'm doing you a favour" manner) then stamped me through.

This is in comparison to my last entry into the US (also at YYZ) where my hair (little longer than I would have liked, but not entirely relevant to the story) kept falling and covering my face before the camera would snap the photo. When I got to the agent, I apologized about the poor photo... the agent was sympathetic, told me it's a common issue and wished me a happy journey...

Depends on why you're avoiding the country. I find there are good and bad everywhere. But if you're polite and confident, in general most countries are fine... it's usually specific to the airport you're going through (eg, avoid Shanghai/Pudong like the plague)

New Zealand 2009. I was on an ultra cheap A380 trip from LHR to AKL via DXB in F with EK. Just did it for the hell of it. Immigration officer at AKL was having none of it when I said I was staying only for 5 days. His “suspicion” intensified when he realised I had been to AKL on the exact same date in 2007. He then asks his “gotcha” question, “Have you got a return ticket”. Out comes the e-ticket itinerary in F. He gave me a look of hell stamped my passport and sent me on my way.

Qatar Airways check-in in Houston:
"Do you have residency? Do you have a visa?" - No, US citizens get a visa waiver.
"Do you have a return flight?" - Yes, I booked it on the same PNR. - "What's a PNR?"

Let it be known that the Qatar immigration authorities seemed to have few fewer issues with me than the Houston ground staff.

Those things count as "issues" in your book?

I never said they were issues for me (they had issues with me), but I think it's ridiculous when airport staff ask questions about processes that aren't correct and don't understand flight reservation terms, like PNR - that is their job, correct?

maybe their focus is on security so that they don’t know terms like PNR IATA IAH (in Houston!) lol
Some airport staff workers are just not always going to be the brightest bulbs. I too hate having to be patient due to a gatekeeping employee’s incompetence.

Not at an airport, but I had to register with the police in Indonesia because I was staying in a private residence, not a hotel. The police office took a casual look at my passport which I saw had flicked open showing an Iranian visa. (I got one of the very last big fancy full-page visas before they stopped putting the visas in passports.) He stopped and looked at it for a very long time. He then started going through my passport page by page looking at each page very carefully. He must have seen my Iraqi (Kurdistan) visa. Eventually he got all the way through and for a while didn't say anything. Then, he completed the documentation and bid me on my way. I do wonder if I might have been questioned more if I wasn't with my sponsor who is the direct boss of the policeman's wife. But, that's just vague wondering. But, I've never ever had a passport scrutinised like that before. (There hasn't been much since as this happened during my most recent journey.)