This is the kind of situation where there is no right/wrong answer, but it is curious way to debut.
I blame anime in general, but I also blame a forementioned Robert Crumb, the crazy bastard...He's great. All the old superhero/Looney Tunes cartoons that I ingested like air as a kid are also to blame. Chuck Jones and Tex Avery especially.
I could come out and say that both Pablo Picasso and Vincent van Gogh have aided.
Webcomickers are heavy influences, and I'm not kissing any ass when I say that Jeph is one of them. Fred Gallagher and Ian MacConville were the first two guys whose style I tried to imitate.