People who just don't care...
People who use normals as a justification to go 0-10 by 10 minutes are the cancer of this game. Seriously. "It's just a normal" isn't an excuse to waste an hour of my time, holding the match hostage when we're 3 kills to their 30 by 12 minutes and we've already lost every tier 2 tower yet all 4 teammates refuse to ff.
I swear, every time I try to go for level 6 and 7 masteries on TF I get a bunch of drunk/high/12 year old/neanderthal players to place a nice roadblock to that goal. Thanks Riot. Thanks for having a game with such a wonderful community, and a matchmaking system that paired me with the best examples.