The point being made, I think, wasn't "Fantasy football is bad" or "Fantasy footballers are jerks", it was "People who make fun of D&D players but play fantasy football themselves are hypocritical". I'm fine with people having fun however they like, but only if they extend me the same courtesy.
On topic, I'm sure this has been mentioned before, but...
Schrodinger's Player
Until the session starts, you don't know if he's coming or not. Often cancels at the last minute, even when he said the time was OK. Anyone can miss an occasional session or have something important come up at the last minute, but this guy does it as often as not. Makes it really hard to have a consistent campaign, when one of the characters keeps popping in and out of existence...