mushroom stamp

plural mushroom stamps

1. humorousslangA mark left by slapping a person with one's penis.

   Those who wipe off the mushroom stamp are only asking for more from my gigantic mushroom stamper!

   2001, MushroomStamper, “mushroom stamps”, in alt.fan.jessica-alba (Usenet)

   2 more examples

   Bell was walking by when he decided to interject. "How about them ole' Batman sounds? Like thwap!" We pondered what that sound could be used for. I made a suggestion, “Like a mushroom stamp?” Every around us laughed at that idea.

   2013, Jared Maxwell, Unsung: Memoirs of an Infantryman, page 112

   It's not a good sign of your gaming prowess when you get your first mushroom stamp from a ten-year-old girl, not simply because I'm sure the act would be physiologically impossible by^([sic]) that aforementioned ten-year-old girl.

   2014, Regan Wolfram, After The Fires Went Out: Descent