Used to indicate an excessively stupid comment or action which neither facepalm or headdesk can adequately describe.
User2: What stuff?
User1: Two squirrels came up to the window and started eating each other!
User1: Or maybe big cats, or possibly two dogs and a chipmunk...
Facedesk is commonly represented by a crude demotivational poster including a picture of a person with their head pressed against a desk and the word Facedesk either on the picture or underneath. This is used as a desperate attempt to enhance the impact of the term.
Facedesk would fit between the more commonly used facepalm and wallbash.
All I do when I think of "online" in GT5 is...
BECAUSE SOMETIMES, PALMS AREN'T ENOUGH