The act of pressing the head of ones penis into another persons forehead or other facial area.
As soon as Ben passed out, Jer proceeded to mushroom stamp him to no avail.
po Snapdragon Август 8, 2003
The male act of stamping the penis into an ink blotter, then proceeding to mark an unsuspecting customer with the "branding" of the mushroom tip.
"Yesterday Sam got ahold of mom's red ink blotter and I woke up to him mushroom stamping me in the face".
po LinzMarie79 Јул 5, 2010