When a girl has a butt that just looks fucking fantastic in pants, but once the pants come off it has so many craters it looks like an astroid.

Can also sometimes been seen when wearing very tight skirts.
Example 1
Girl 1: Ugh, she has such an astroid ass! Everyone thinks it looks so nice, but it's really not that nice!
Girl 2: I know dude, I saw that shit in the locker room the other day!
Example 2
Student 1: Dude, Ms D has such a nice ass!
Student 2: It's not that nice dude, wait until she turns around in that tight skirt. That shit's an astroid ass!
by BagFullOfBlowjobs December 13, 2014
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