Create an ADD TO FOE list!
Sometimes you play with nice people, great teamplayers, so you add them to your friends.
Sometimes you play with such idiots, or just people that don't fit with your play style, that you do not ever want to play with them again.
That is where the ADD TO FOE feature comes in.
Exactly the same as ADD FRIEND, but ADD FOE. Someone who is your foe will never get to play with you in any matchup, draft, random pick or WHATEVER.
You could even add a MATCH ME AGAINST MY FOE feature.
What do you think?