That wasn't one of the specials, kiddo. (Via)
The photobomb is so pervasive online, there should be a separate Internet set aside just for their viewing. They come in all varieties, but they are not all alike. There's the low-level, intentional "I'm gonna eff up your pic with my dumb face" photobomb. There's the dichotomous photobomb, where the foreground and background are at direct odds with each other, but this usually involves little more than someone in the background happily living life who just happens to not fit into the intended foreground pose.