I have to say the downright stupidest thing I heard was from a Manchester United fan outside Old Trafford. Now I support Man Utd too but this comment was ridiculous. It was to do with the half and half football scarfs (on this occasion it was the Man Utd vs Man City game)
"Why the hell would someone want to have a scarf which has the other teams names on it, they aren't proper fans those people"
Then he said something racist but his IQ before even that was clearly very, very poor.