Every single mexican in Red Dead Redemption. Being mexican myself, I can say that not only those "mexicans" speak a very weird spanish, full of phonetical AND grammatical errors... but also their english is incredibly awful. (I mean, I know not many mexicans speak with perfect english accent, but dear god... that was just awful)
Actually, that was the only thing I despised about the game. Until I got to Mexico, I thought the game was really awesome. But the second a "mexican" opened his mouth, I had to turn off the console. The awful english I can forgive... but I really thought that Rockstar would, at least, hire voice actors that actually spoke spanish, instead of people that only read a badly written script. (Just the spanish parts. After I got out of Mexico the game returned to be really awesome =P)
(PS: Forgive my english, if anything I said is grammatically wrong... I'm still learning =P)