A Herpderpington is an
individual who enjoys
photobombing people's photos by making the typical Herp Derp face (or
equivalent). This can either be done as a joke to be funny, or done to be an asshole. Usually, Herpderpingtons act as a group, so the name comes from a play on words on a family name or last name.
It is also the official title for those who herp derp.