I've seen a couple of bad ones recently too.

73X , I'm sitting in F and overheads are pretty full by the time the last F passenger is boarding behind the BG5 people. BG5 guy sees a space over 3B and stashes his roller-board and walks towards the back. Guy two people behind him say "Sir, sir, please can you get your bag out from that overhead because that's where I'm sitting and its the last space in FC". BG5 guys looks back and keeps walking, so the F passenger asks the FA to move BG5's bag somewhere else. She tells him "Its against the rules for us to move a passengers bag", to which he laughs and says "I see you move bags all the time, that's a ridiculous statement". Steely eyed stare from FA who suggests he look for space in the back and, if none is available, she'll see if it will fit in the closet. Another passenger in F volunteered to put their briefcase under the seat, so problem solved itself, no thanks to the FA. The guy was seriously annoyed and commiserated with the passenger next to him about how far UA has fallen of late.

The other recent one was a 22" roller-board, wheeled "briefcase" stacked on top and a backpack over the shoulder. Guy stowed all three in the overhead bin right in front of the FA who apparently couldn't have cared less.