You know, people have mentioned Garithos from WC3 a lot, and I have to agree, I had an intense, physical reaction to this asshole. He really pissed me off.
Every single damned Marine from Halo 3, except Johnson. They're fighting for the survival of their planet, nay, their SPECIES, and they stand there spouting one liners.
The Companion Cube from Portal. The thing wouldn't shut up.
Geodude from Pokemon. 'Geo', meaning rock, and 'dude' thrown together? How much more unoriginal can you get. In fact, all the damned Pokemon piss me off. Their names consist of Japanese pronunciations or puns, and their speech consists of their name over and over.
Waluigi and Wario. Ugly, pathetic ripoffs who exist to milk more money from nostalgic Mario/Luigi fans.
Any game that features a big, muscular white guy or any JRPG also gets the 'failpit' as bad characters.