Chivalry. Only game I've ever audibly sworn at. Sometimes you see the tip of an enemy's blade swing past you, completely missing you, and you still take damage. Lookdown overheads, too, are pretty much unblockable, deaths are nearly always frustrating and no matter what happened, it always feels like the game's fault and not yours. Lag is handled horribly, and if I'm sitting on top of a server I might get 28 ping whereas I get in the lower teens in any Valve game. Horrible design decisions, such as going colorblind when you lose health, contribute to teamkills, as does blood-soaked warriors looking exactly like the red-clad enemies. Movement is clunky, you get stuck on random bits of terrain, combat on anything but a flat surface is screwed up, kicks are clunky, mechanics that should be there are not in favor of "balance." Also, players tend to spam the chat with crap talk, vote to kick anyone who manages to kill them, and then proceed to play horribly and team-kill a lot.
Have I mentioned that it's one of my favorite games?
Also, World of Warcraft, though it just made me sad instead of rage. I joined a private server after a couple hours of playing retail and decided I wasn't about to face the grind. So a friend took me to a place to climb a castle, and he got ganked by a bunch of guys in a non-PVP area. I healed him, as a priest should, and they reported me for doing so, even after I asked them several times what I was doing wrong.
I haven't played since, and realize now why I preferred single-player games for so long.