Quite a few years ago, the flight crew let me sit in for the landing (LHR-DXB). Were vectored round the houses for the approach, but got on the ground, thanking the crew and was about to leave when the door opens and this pax walks in. Introduces himself and says he was watching the approach on the video feed, and starts telling the crew how he would have done it! After he's finished, the skipper asked him if he had ever heard of ATC, to which the guy replied:
"Of course I have. I have a PPL you know!"
Hats off to the skipper for not thumping him.
Cheers.