pigs are fuckin' evil. they will eat people (even if they're alive). I had a relative that was eaten alive by one. he had a heart attack, felled down, and the pigs went at him.
Gonna second goats. Most of the rest can be excused as just being stupid - cows are lumbering morons for example. Goats are malicious little bastards though.
I know some people keep turkeys on farms. Turkeys are fucking dicks. When I was a kid I helped work on a farm sanctuary that had like three of them, and everytime I'd come in to clean their stuff they'd nip at me and puff out their feathers like assholes. They also chase you (and probably have fun doing so). Learned that the hard way.