A massive cyst on your bum that either bursts or is surgically removed leaving a crater on your bum.
Omg duuuude! My brother had the biggest bum bomb, seriously, it left a Grand Canyon sized crater down there!
by Golden Seagul July 20, 2018
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A bomb shoved up someone's ass.
AAAHHH THAT GUY HAS A BUM BOMB! Save Me!
by Steaver370 April 26, 2004
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