Was once on a B757 from Manchester to Heathrow, sitting just behind the wing. Pilot initiated a very early go-around as the flaps wouldn't extend and I was very amused to hear him make a PA explaining that ATC had asked him to go around.
After a flapless landing and taxiing back to the terminal, followed by a number of emergency vehicles, I swear I was the only pax onboard who had any idea what had happened!