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The end part of a mans penis which is so hardand sore it eventually looks like a mushroom.
Me -"CRIST! Look at that germans bell!"
My bro -"Mushroom helmet!"
*everyone watching german porn laughs*
by GirlSkater May 02, 2004
The head of a mans dick
Can you make my mushroom helmet touch your tonsils?
by smitty December 20, 2002