I've tried joining games and being blocked because on of the players Enemied me. I never know why because I never ask. It's weird. Talking to other players on here it seems like most of the time it's because of perceived slights. Somebody thought you were ganging up on him, or you declined an offer to team-up in a game. Fairly silly, reasons I get the impression.
Hey man, I don't think it's me who listed you as enemy. When I check your profile it says you're listed as "Neither".
If you visit my profile does it say I'm listed as Enemy?