League of Legends, Heroes of Newerth, Defense of the Ancients, DOTA 2, Demigod, etc.
They're fun games with friends, but playing them alone is like drilling your own teeth. They're team based PvP games, and one person on a team can ruin the entire game.
It you're doing well in a game, you'll always get one guy in your team that either doesn't know what he's doing or is playing just to troll the team. If you're doing bad (Hell, if you make just one mistake), you'll always have someone on your team screaming FUCKING NOOB COST US THE GAME YOU SUCK UNINSTALL RAGE.
It really doesn't help that a lot of the genre's mechanics are weird, outdated, or not explained in game at all, so you have to rely on the community to explain things.
...geez, why am I still playing League of Legends again?