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1.
n. When the fabric on the butt of jeans stretches and no longer fits tightly. Called "diaper butt" because of the baggy appearance, similar to a diaper full of poop.
Term can be applied to swim suits.
"Aw man, I haven't washed these pants in about 3 days. They're all stretched out and look like diaper butt."
by max636 May 18, 2008
 
2.
(n). Pants that sag in the butt area causing what appears to be a diaper like appearance.
Excess fabric in the butt area, that is not filled out by the butt of the wearer.
This problem frequently occurs on girls who have no butt and are wearing pants that leave room for girls who do. The pants are usual a cotton material, and are not form fitting. Diaper butt usually causes feelings of self-consciousness and embarrassment. Diaper butt is not desirable and is extremely unattractive.
Girls say: "Do these pants give me diaper butt?"
Guys would say, "Oh man, did you see that girl's diaper butt?
by Harnagel March 03, 2009
 
3.
What a guy's butt looks like when they sag their pants. Another reason for wearing pants properly. Gives the appearance of the football player in question having pooped his pants.
"Ewwwwww! He has a diaper butt!!!!"
by Lizard Butt September 09, 2011
 
4.
When a person gets butt implants that are too big for their body structure and it makes them look like they are wearing a diaper.
Did you see that celebrity that just got the implants it gave her a diaper butt
by Takkat June 03, 2014
 
5.
A womans backside that is bulky with the appearance of wearing a diaper. Usually caused by large bulky underwear, body fat, mom jeans or just being old.
That girl you were chatting up had a cute face but had some major diaper butt.
by melvin cutter February 02, 2009