This week, flight out of FAT, which was apparently 100% full, GA is onboard with the FA:

FA: Dang, the manifest says 76, and I only count 75 passengers. What's up with that?
GA: Well, that would be nice, because I have a <nonrev> I'd like to place in that open seat.
FA: Hmm. I will go back and ask (walks down isle)
FA: (returns) He says he bought the seat next to him.
GA: ??? Oh, I see it now. Nope, that's his seat.
GA: (walks off aircraft and can be heard talking) Sorry, there's literally no seats on the airplane left.

Closed the door and off we went.

All the best, James