The facial expression equivalent of honking someone with a car horn.
Used for expressing displeasure towards the actions of a rude, obnoxious or annoying person.
It does not always have to be directed towards the offending person but can be used as a means of expressing your displeasure to others, as a means of attracting empathy.
There is a FACEBOOK group for users of the facehorn (with explanatory photos) which anyone can join: "dont make me face horn you"
"Facehorn ": When someone pushes infront of you in a queue, bumps into you on the sidewalk, decides to leave a party early, or generally makes a dick move etc etc
It can also be used in conversation:
"I dont think ultimate frisbee is a sport"
It can also be used as an abbreviation in online chat:
"I dont think Miranda Kerr is hot"
most people know of the term 'facepalm' (if not, see facepalm pre-reading this)
facehorn is a derivative of this action whereby the horn of a car is activated by the slamming of face on steering wheel. This is generally in reaction to someone doing something fucking stupid (earning a facepalm) which results in them being a cunt on the road (earning a horn blast).
the facehorn allows the road user to encapsulate two reactive emotions in one fell swoop saving both time and energy.
quite simply something such as a person turning the wrong way down a one way street resulting in a traffic jam. - you facehorn
another example is when someone goes straight when the green turning light comes on. - you facehorn