Yeah I have come across that dude before, he is a stunt-flyer at airshows.....he flies the plane imitating that he is drunk/crazy etc (like some he will have door open and put part arms and legs etc hanging out of it as he's flying) ...they do a routine on the ground etc just like that (where he "hijacks" it etc).
This kind of routine is also found in lesser way in other airshows ( for example at hamilton airshow I saw one guy do a bit of it with a Beech 18 iirc, where it was called an "elephant dance"...they even had the song from the movie "Dumbo" for it)....this dude just took it to an extreme and seemingly spontaneous level.
Did some searches just to see I am not losing my memory lol:
Here is the beech 18 routine I am talking about:
Here is this "drunk" dude doing routine elsewhere:
You actually have to be a really good pilot to do this stuff, ironically heh.