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1.
Condition which occurs when too small of a bra size is worn, effectively dissecting the breasts and giving the appearance of 4 boobs.
Girl, you need a bigger bra, that quadriboob is awful.
by gg May 13, 2004
 
2.
When one's ribs are showing almost as much as their breasts, especially in tight fitting clothes, it appears they have four boobs, or quadriboobs.
Dude, don't wear that shirt. It makes you have quadriboobs.
by MMMTI January 28, 2009