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1.
Gravity Bomb, (or G-Bomb), Refers to when a person, usually male, goes to the toilet and drops a massive shit into the bowl. This 'massive shit' usually descends from the asshole as one massive, sphere-shaped, ball that explodes into the water with its own unique sound according to the manner in which the G-Bomber has pushed out his/her G-Bomb
He went to the toilet and dropped a massive Gravity Bomb
by OmNomNomInc. February 08, 2010
 
2.
taking a hard spill, fall or wreck
I couldn't stay on my board today, I was dropping gravity bomb's all over the mountain!
by sks4540 April 19, 2004