I've had mostly good experiences on airlines, (haven't flown Ryan air yet) but sometimes the true douchebaggery seems to come out in droves....
On southwest one I had an incident where I boarded, got a window seat in the back of the plane, put my magazine and MP3 player in the seatback, then got up to hit the head real quick. When I came back to my seat some guy was sitting in my seat, my backpack was under his feet and my stuff was still in the seat back. After pointing out the obvious that it was my stuff and my seat, he said oh well and just sat there. Asked again...nothing. There were still seats open, so I just figured I'd go somewhere else...since this guy wasn't going to move. I then asked for him to give me my stuff, and he said it was his!!!! WTF?? Luckily the 50+ year old flight attendant (the type you don't fck with) saw the whole thing and kick the dude out and up to some middle seat.
Douche!
edit for "douchebaggery"