A word made by combining the words "head" and "drop" to describe the action of dropping one's own head in response to a sarcastic remark.
John: Paris Hilton is fat, Kanye West has terrible lyrics, Lil Wayne's flow is terrible, Lady Gaga isn't weird at all, Justin Bieber has a low voice, and Birdman never talks about money.
The motion of suddenly lowering oneself's head in response to a sarcastic remark. In text, it is conventionally set off with asterisks.
Joey: Dude, Birdman never raps about expensive cars and money.