Recently, on a flight between Bangkok and Taipei, our flight was delayed by an hour because a passenger had cancelled his ticket while the doors were still open (he was already seated; I saw him run to the front and dart off the plane). We had to leave the plane for about twenty minutes while bags were verified.

Has this happened to anyone?

Not quite that bad, but I have had flights delayed because people checked in then never boarded and the airline had to off load their bags.

Somewhat similar happened to me on a LH flight from LAX to MUC. One of the last persons to board was a young woman, who realized a minute or two after arriving at her seat, that her boyfriend did not clear the standby list. She insisted on getting off the plane to be with him. This caused a good twenty minute delay while they pulled luggage, and boarded a different young woman who was on standby.

I was sitting right next to the boarding door, and the two flight attendants standing at the door were quite perturbed about the disruption. Ultimately the flight arrived in MUC about 25 minutes late.

I have had a couple of occasions where a nervous traveler decided he just could not handle flying that day after boarding. Not so dramatic as the above. In both cases, the pax was simply deboarded. Both resulted in delays but not terribly bad.

I did it myself once. Sat down and became violently ill, so I deboarded. It did cause a delay.

I was also the cause of a delay on one occasion.

A QF domestic flight on which I took quite regularly, regularly enough I knew some of the Flight Attendants, boarded was seated in 1D in J class and just as the door was about to be closed I got a call that my wife had gone into early labor and was being admitted for an emergency caesarian.

The lead FA was very helpful in getting things arranged for me to disembark, but it did delay the flight somewhat.

Took the flight two weeks later and got the same lead FA who of course wanted to see the photos of the addition to the family.

Slightly different example but flying MCO to LGW a few weeks back with VS.

We take this route a few times each year and the gate lice are awful every time but on this occasion they got 'rewarded'. Gate agent announced the start of boarding followed by the invite for EVERYONE to board and this would be the only boarding announcement.

Flight was 2/3 full at best but resulted in some PAX in Upper Class to march up to the gate desk and demand them to fast track them through the madness.

Also when flying BHD they call the gate number and there is a short walk to the gate. Always get a few 'run' towards the gate only to hold everyone up when they have to dig out their ticket / ID.

Any correlation to your username?

Yes, 3 months ago on a BRU-FRA-VIE-DOH-BKK-UTH routing
It was a mileage run.
We were all seated at BRU and ready to go when a passenger decided to get off the plane.
Captain explained this and told us we would be delayed some time to find and unload passenger's bag. This took more than 15 minutes and we heard people rumbling in the plane's belly.
Captain came back online several times to explain the situation.
I had a 2h connection time at FRA.
At last they found and removed the guys bag but the captain then announced further bad news: we lost our gate at FRA, he sounded very very upset, so were many passengers.
A few minutes later he announced we would need to wait an extra 2h for a gate......
There went the rest of my trip down the drain and a lot of trouble ahead.
Then 5 minute later he told us OK, we are getting out of here NOW.
Even when taxiing I was not sure we would leave BRU ground, but we did.
Landing FRA my flight to VIE had 30 minutes left (bags were checked in to VIE) and was leaving next gate, that was the best and shortest walk to a gate ever.
I very much hope never to plan such a mileage run again

Does discoverying that one is on wrong plane counts? One guy had mad dash out when found out that.

How does that even work, especially on something like an A380? Does the airline have a vague idea of where the person's bag is in the hold, or do they have to go through each and every bag until they find it?

3-4 times in 28 years of travel. One time was a colleague who 'forgot' to tell us he was scared of flying, Right up to the point when he stood up, muttered "I can't do this!" and exited the plane towards the end of boarding. Bag reconciliation and the resulting delay is the main problem.

They know which LD container it is in. For long haul the bags are in containers. For shorthaul no, they have to go through each bag as they are stacked in the hold.

A couple of years ago I saw a couple with a ~3 year old child at the gate. When they called families the father boarded with the kid but mom didn't. The kid started a tantrum because he didn't want to be separated from the mom. I board 10 minutes later and guess where the kid is? This kid threw a tantrum like I've never seen. Kicking, thrashing, screaming, went on for over 20 minutes after I boarded. The kid was thrashing around so much they couldn't get him belted in, so they were eventually off loaded, and many of the rest of us missed connections.

Happened on my one and only Concorde flight (LHR-JFK). We were late due to weather in New York and once we were all aboard a gate agent came in and spoke with a passenger who then disembarked, looking jovial the whole time. Turns out his company had contacted BA (this was before cell phones were ubiquitous) to tell the passenger not to bother going to NYC.

Didn't delay the flight further, as I suspect no checked luggage was involved.