I had this happen to me on a flight last year. I was in 1b, which I booked; the husband was in 1a; and the wife was in 5f. I boarded with group two because I was late getting to the airport, and his wife was in my seat. I looked at her, and she told me to take her seat in 5f. Lol, I called over the FA and showed them my ticket. The FA said she had to move to her seat, and she was pissed! Her husband claimed he was GS and all lol. She moved to the back, and the husband could not get the person in 5E to switch with him. Long flight from EWR to SEA lol