The Rice University Neologisms Database

To bang one's face on the desk directly in front of them, esp. in frustration; to slump onto the desk in frustration; to be incredibly frustrated. The term 'headdesk' refers to a specific action, that of a person 'banging their head upon the desk in frustration'. The preceding phrase was shortened to 'headdesk' because it is much easier and quicker to type than the whole phrase. It was then metonymically extended to not only refer to the actual action, but the state of frustration that accompanied or prompted the action. It is very similar to the term 'facepalm' and was also used by originally gamers but has since spread to almost anyone who surfs the internet frequently. It is typically used by itself as an interjection, as opposed to within a sentence, as the one word now denotes a whole sentence something along the lines of "I'm banging my head against my desk in frustration", but can be used as a verb, although this is very unusual.