Although this doesn't quite compare to some of the other stories on this thread it still amazes me when I think back to it.
Last year I agreed to take an old friend for a flight over to Gloucester then for a quick bit of sightseeing over our old home town before going to look at Silverstone etc as he'd been asking for ages. The first hint of a bad day came when I was re-fuelling the plane before the flight and he came over and asked me in a rather loud voice "are all pilots geeks then?"
I rather curtly replied no and thanks very much for that insightful comment but maybe we should get going before we get lynched.
Things went ok after that until I asked him if he was enjoying it to which he replied "well, yeah it's ok but not very comfortable" I personally think PA28's can be quite comfortable with only 2up (I'm not that big!)
At Gloucester, ready to make my call for the return leg, and suddenly the control yoke moves fast back towards me and then starts waggling around. Quick look across to find my friend helpfully 'checking controls for full free movement!' shortly followed by some pressing of buttons on the radio stack. I decided at this point that we were going to head straight home, tried to get a zone transit through Brize and was told to remain clear etc so as I replied I hear my friend pipe up with 'Why can't you tell those f*****s to b****r off!' Thankfully I managed to let go off the ptt switch quickly enough before the swearing started.
Thankfully the rest of the flight went uneventfully but it will be a long time before we go up again!