Unfortunately I had the opposite experience on UA294 this week. I was seated in 11C, an exit row and the last row of E+ on the A320. The person behind me was very unhappy about not having enough leg room, and decided to take it out on me by constantly bothering me. I was trying to sleep and he kept kicking my seat, waking me up and asking me to move my seat upright while he got in and out of the seat (seemingly every 10 minutes), and also just complaining loudly about how much his seat sucked.

Then he went to the people across the ailse for me, where 11E was unoccupied, and asked if he could sit there. Those pax were clearly not happy about the prospect of having him sit there, and so said "no, you're not really supposed to do that." Then the troublesome pax asked the FA if he could sit there, and she said yes, so he did. Even though it was an exit row, she didn't even ask him if he'd be willing to assist in the event of an emergency evacuation.

I can't complain too much because I was glad to get this guy further away from me, but I would have been pretty unhappy to have the FA seat someone unpleasant like that next to me, especially when I previously had an empty seat there.