A picture is worth a thousand words.
This is an example of photobomb. A photobomb occurs when something in the background totally steals the show of what a photograph was supposed to be about. The subject is often clueless of what is going on, either smiling wide or trying to appear sultry, unaware that guys are mooning the camera or dogs are humping.
This is Photobomb is a website featuring nothing else. Some of the pictures are a little graphic; there is also a PG rated or less version.