Not really horror stories but more like "what the what?" stories -

In first, on the way home from the Caribbean, after we board I discover our seats have been shifted due to a change in aircraft. Not a big deal since we had two of the three seats adjoining each other, or so I think.

Turns out a man is sitting in my son's seat and refuses to move because he wants to sit next to his wife. He keeps insisting that I move my then 6yo son back two rows, where he would have been sitting without me or my husband to supervise him. (He was sitting in my son's seat.) It finally ended with me yelling at him. He and the wife jumped up and moved to the back of the cabin. Eventually, enough people shuffled around and they sat together. In hindsight, I should not have engaged him and just went straight to the FA.

Same route, earlier this year - A man and woman board behind us. The wife is dressed very strangely for the weather - long pants, turtleneck sweater, floor length wool coat and a huge scarf wrapped around her neck in 90 degree weather. She follows her husband, who is seated next to my husband, and stands in the aisle. Just stands there. After a while, her husband screams at her to "go sit in your seat!" several times over and then starts ranting at her how it doesn't matter where she sits, that she is going to just fall asleep right away. She sulks off and sits in the first row, against the window. He then turns to my husband and starts ranting about how she wanted him (her husband) to ask my husband to switch seats and why the f_ck does she need to sit next to him and so on. After he downed his beverage, he took off his shoes and slept most of the flight.

I don't switch because I always sit next to our son but my husband will often switch as long as the trade is even-up.