To slap someone across the face with one's penis.
Those dudes are always mushroom slapping each other.
by Nate Fergus February 3, 2003
if someone happens to be getting fresh with you, mushroom slap them. This means pulling out your jimmy and making solid contact with their facial region.
C-dav definitely mushroom slapped that girl last period because she said "oh my gosh guys guess what happened?"
by drew s April 12, 2004
Being slapped with a wang. Usually a hard wang.
"So this chick was blowin' some guy one day, and he pulled out and gave her a mushroom slap!"
by D.Socko May 9, 2004
When you slap someone with your soft circumcised penis causing a small red mushroom shaped mark on the skin from the head of the penis.
Dude I mushroom slapped her last night right on the cheek, it left a red mark!
by Aiden07321 June 6, 2010
When a guy takes his hard dick, and swings it as hard as he can, hitting a person (hopefully a girl) on her body with his mushroom. If done correctly it will leave a mushroom imprint for several minutes with a lasting red spot afterwards.

(not easy to do)
ex) mushroom slap her in the face and it will leave a mark. very funny. total ownage
by Mushroom slap 696969 May 15, 2009
When u slap a bitch so hard with ur pee pee that she gets goes retarded
I herd Jenny got the mushroom slap of death now she’s in in special ed class
by Grass man December 11, 2019
After having anal sex to slap someone across the face with one's penis leaving a rectal juice mark. mushroom slap
James:"Hey Ron what happened to Adee's face?"
Rondel:"After taking her ass virginity, I gave her a chocolate mushroom slap and I guess I left a mark."
by James izzle April 14, 2005