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When the seat of your jeans is baggy so it makes you look like you have a saggy diaper. Can be fixed by buying a better fitting pair of pants that hugs your butt.

Can be abbreviated as SBS.
-Dude, you see that chick?
-Yeah man, either she needs to hit the gym or those jeans are just giving her Saggy Butt Syndrome!
by Gilli2 June 29, 2010