Canada, easily. Back in my early days of FT, there was a fare SMF-HKG on AC for $400 or so, so I booked it and planned to spend 3 days in Hong Kong. It was basically a vacation run -- happy to earn lots of miles for cheap and might as well stay for a few days. All went fine until I had to clear immigration in YVR and they had lots of questions:

Why is a 25 year old flying to Hong Kong for only three days? (Cuz I felt like it.)
Why are you connecting in Canada? (Because the cheap flight was on Air Canada.)
What are you doing when you're there? (Being a tourist.)
Are you coming back to Canada soon? (Yes, because the flight back is also on Air Canada.)

I got held in a room for about 90 minutes while they checked every bit of my luggage. Thankfully I had a 3 hour layover and then there was a delay anyway, so it made it moot. Great first impression of flying in Canada!

Switzerland (if you're a minority). I went on a train as part of a conference and had a poster to present at the meeting in my hand. They came straight for me as the train approached the border, interrogated me in front of everyone on the train, searched all my bags and damaged my poster. Soured my entire opinion of the country.

Check Point Charlie, 1967. We had gone over to East Berlin for the day and were coming back. I guess it looked like fun for the East German guards to harass two teen-age girls. They took our passports, held us for over an hour, periodically coming into the room and yelling at us in German, which unfortunately, we spoke very little of.

Finally, they gave us our passports and we walked over to the West checkpoint, where the U.S. Marine guards explained that random people get harassed just for the "fun" of it. We obviously had won the lottery that day.

Also a Checkpoint Charlie story: In 1982 I was traveling on a (US) diplomatic passport, which allowed allied military and diplomats to move freely in all 4 zones of Berlin (then still operating under occupation rules) without hindrance. The Soviets allowed the East Germans to control their borders, allowing them to make believe that they actually controlled the situation. The East German border guards always tried to grab our diplomatic passports and impress them with entry/departure stamps, and we had to hold onto them to prevent this pseudo-recognition of East German sovereignty over East Berlin. It was always loads of fun, and everyone knew it was a game, but it was all rather good-natured.

Saw racist passport control nonsense hit soon after the bridge between Denmark and Sweden had opened for rail passengers. The Swedish government would sometimes staff Malmo with one or two people to play border guard and the border guard on the platform would literally make a bee-line straight to those they assumed were of non-European ethnic heritage. And sort of the same thing on the trains at time, but under color of customs control. Some Americans of perceived African, Asian and Latin American descent who happened to be earlier users of the bridge from Denmark to Sweden would sometimes be the only Americans (in the groups or even when alone) to get hit by demands to show passports in Malmo while perceived European Americans and other (non-NPU) Europeans alongside them got ignored by the border control guards. And in those days it would be like "oh, you must be adopted" if sounding like an American or Canadian after showing the passports.

Passport control experiences speak very much to the state of prejudice which a state and its society -- wittingly or otherwise -- host and support.

Yup, it certainly didn’t stop at the border in Switzerland for me. I’ve avoided the country ever since (and that was over 20 years ago).

I had a very lengthy examination of my passport by a US immigration officer and then what seemed to be a supervising officer at SNN (there is pre-clearance at SNN, or at any rate there was at the time). They looked at it multiple times, shining a light at different angles and seemed to be using something similar to a magnifying glass, looking for evidence of tampering. They took me aside to some office and it lasted a good half hour. They asked me multiple questions as to why I was flying from SNN. I guess SNN had little traffic at the time from pax who did not have an Irish, British or US passport so my passport from a mainland EU country was perhaps part of what was making me suspicious in their eyes. They never searched me personally; it was just the passport they were examining. My travel companion was Irish and had got onboard without problem but it was getting to the stage where I thought that they would keep me past the departure time and was starting to think about the complications as I had made all the bookings for the holiday, which were mostly in my name and booked with my credit cards. They eventually let me go. I ran and just about made it onboard before they closed the flight.

good. I would do same. I’m American and I refuse to travel to certain states in USA itself :-)

Switzerland. The only time I was questioned with the US passport. The story is that I with my German colleagues traveled to Zurich in a car to our Switzerland office for a day and then come back.

On our way back we were stopped at passport control. My German colleagues' passports were no interest however my US passport caused additional questions, including - 'what have you been doing in Switzerland'. On our answer - visiting our office - caused 30 min delay to check if I violated Swiss rules by performing work in Switzerland without a work permit. I was told that next time I am planning to stay in Switzerland for more than 72 hours while going to the office, I need to obtain a work permit first.

So the solution for me is easy - when I go to Switzerland, if I am asked 'why are you here/what have you been doing here?' I answer - 'shopping for Rolex'.

If they said that they are staying there for frog porridge, there would be no questions asked.

I've had two interesting experiences:

• Canada - YTZ - The border services officer was asking why I was coming to Canada. I replied for tourism, and somehow, my big mouth started talking about trying out hotels. He asked how many hotels I was staying at and I told him I switch every day. He then asked why I would want to do that, and I explained my fascination with hotels since watching Samantha Brown on the Travel Channel as a little kid. We ended up laughing - he said he knew I must have a story :-)
• Not passport control, but the airline security officer for Aeromexico at MEX wanted to know how I had lost so much weight from my passport photo and if it was from diet or exercise and how much I had lost and to keep up the good work :-)

I had a similar Sfo passport story due to weight loss. The agent was around my age range and asked about my size not fully matching my photo. I said that I joined a gym and went almost daily; he asked the name (24 hour fitness) and acted interested.

I used to love Travel Channel shows with Samantha brown and Justine Shapiro :-) I don’t even know if that network now exists.

It does but focuses on paranormal shows - not sure how that relates to Travel ;-)

Wow, that's crazy, never thought that would happen in Switzerland. Had a breeze there for 2 weeks, via airport though.

Before Global Entry, had a bewildering encounter entering USA (I think at DTW) with an officer who could not understand why I was returning from Bangkok via Europe.
I could not get him to grasp that it is on the opposite side of the world, so is the same distance / time when compared to TPAC routing.

Global Entry forever!