I personally don't find this to be great. It looks like you have a lot of better stuff. This is still definitely a good picture. It's just funny. I was expecting a little bit more, though. I can see how this would be a T-shirt design.
Wait, maybe it would work better as a collared shirt design? There's a big difference. Your artwork kind of reminds me of "Regular Show". I guess it's just something with the head size. The little details are good.