Modern Warfare 2- No more dedicated servers means you're all but anonymous. The things that blocked noob tube spam and other minimal skill kill kits are gone. Doesn't help that the guns are horridly balanced.
Fan Sites- Sonic's probably the worst both in terms of blind devotion and "wtf?" factor.
Furry website- see above. Its a fan site at heart, even if they claim its not.
4chan- You can't not mention it. It's a far cry from the hate machine it was when it first hit the web but there's still enough newfags (that's their term by the way) running around in there to make the gears turn.
Facebook- Its the internet, just with your friends, and you get to see far more than you ever wanted to know. Women become whores. Men become fucktards. There's a good reason I'm dead opposed to ever actually using my facebook.
HoN / LoL / DOTA- I made it a point of order to troll teams who'd try to ***** at me any game. Sad thing was that it was almost every single game. Nothing quite says, "I love you." like clogging the voice chat with foreign languages (I think it was Spanish or Portuguese) and then taking the opportunity to ***** at people in English to let them know they screwed up.
WoW- having played it since near-release I can say the community's gone pretty far down hill and Blizzard's only demonstrated that they don't understand their community at all with doozies like the cross-server dungeon system. Four years ago you'd never hear a verbal complaint about low DPS so long as they were doing their jobs but just last month I had a druid try to force (IE: He was healing, and refused to continue) me out of a group because my fresh-to-80 wasn't min / maxing to do "good" DPS.