Once when returning from the US, I was on a Delta flight (out of Cincinnati, IIRC) and having not pre-booked a seat, got allocated a seat at checkin.
I cannot remember the aircraft type, but the seating was 2 - 5 - 2.
The only seat they had was the very, very back of the aircraft, like row 49. In the middle of the 5. On either side were two families of 4, with two kids sitting either side of me. The seat would not recline fully, being the back row. The toilets, which were only feet away, stank to high heaven. And the kids balled, screamed, cried and climbed on me for the entire flight.
Never, ever again.