When you dip your dick in ink, and then proceed to smack it on a girls face while she's sleeping. She'll see the imprint in the morning, and be surprised by the mushroom stamp.
by Sir Stampalot February 9, 2009
The act of sneaking up on someone and slapping them with your penis hard enough so that it leaves a "mushroom" type bruise.
by Bill45421 May 12, 2006