Pitbulls have a tough reputation, but this one is a pushover: he might be afraid of farts.
The pitbull in question is Bullit [sic]. He's the star of a 2009 YouTube video that resurfaced recently on Reddit. Over the course of a minute, he's subjected to various fart noises that appear to emanate from off camera.
If his owner is actually farting, Bullit's fear might be justified. But in any case, the dog's reaction is pretty brilliant.
Although, it's not as great as this French bulldog who is scared of his own farts.
Pitbulls are also afraid of pineapples, by the way.