I've blacklisted a few people, but Masterbrat and Granny Vicky are at the top of my "I will never play a game with them ever" list. Masterbrat has/had a bad habit of leaving games and cursing people out, and Granny Vicky I blacklisted like 20 minutes ago...he/she is a newb, and while that doesn't mean much, I got some horrible positioning in a game, he/she surrendered after a few turns and then proceeded to also curse me out.
http://WarLight.net/MultiPlayer.aspx?GameID=1182776
I did get a little nasty back at him, given, but I think it was earned from their sudden and pointless outburst.