I had an DC-Frankfurt, Germany flight once where I was at the window and a HUGE guy with cane came down the aisle (barely fit down the aisle) sat down next to me. He was a heavy mouth-breather and rolled halfway into my seat as well as taking his own. I was crunched up against the window, having only 1/2 a seat left for myself and the flight hadn’t even taken off yet. I told the stewardess that she had to move me to first class, or find me another seat. Fortunately there was a spare in the tail, where there are only 2 seats per side and I had tons of room. The toilet smell was bad, but it was worth it.
When he sat in front of me the seat went back like it was reclined. Talked to the attendant and offered to sit in a flight seat with them. No where to go. The plane got off the ground and he reclined the seat. Bathroom trip was liking climbing out of a can of sardines. Needed the jaws of life.
Worse was a flight San Diego to Hawaii. Women and small child in the row. Anther kid in front of her. The kids squealed, screamed and cried the whole way. People yelling at the woman and she said "There's nothing I can do." One guy cussed and yelled and they gave him the last seat in first class. The attendants were too passive. Wrote a letter to the airline and got a canned response. My theory. Throw the mom or one of the kids out of the emergency door at 30,000 ft and the other two would behave. No jury would have convicted me. But I let my wife talk me out of it.