I once went to Fulham with an American relative quite well versed in football and knowing full well he shouldn’t cheer an away goal, but he did anyway - being in a quieter part of the ground he got a bit of verbal abuse and nothing much more. Later on Fulham equalised and people swarmed over to celebrate with in his face, but by then he had decided to celebrate Fulham’s goal as well and was jumping about like a lunatic. Cue much confusion among the home fans and I think everyone just thought he wasn’t all there and left him alone after that.