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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
To slap someone across the face with one's penis.
Those dudes are always mushroom slapping each other.
by Nate Fergus February 02, 2003
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 08, 2004
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 14, 2009