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A nuclear explosion or an atomic bomb, which makes a mushroom shaped cloud.
"I saw a documentary about shroom booms on the History channel the other day."
by Orly Wild August 26, 2008
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Soft and offensive. Just like you.

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Man grasps the base of his erection, squeezing, causing the tip of his penis to resemble a mushroom.
While watching the Oprah Winfrey show, i had a hankerin' for a Shroom Boom
by Koonjam and TheBigSmooth December 07, 2009
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Cleveland Steamer Plush

The vengeful act of crapping on a lover's chest while they sleep.

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