When you have a rear end that's so soft, gropeable, and fat that each buttcheek feels like giant, smooth marshmallows.
"I could use your marshmallow ass as a memory foam pillow all night long!"
by Spanky Frank October 07, 2016
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A fat ass girl who has a big ass. Not just a big ass, but a HUGE pale, white ass!
Ew! Look at that marshmallow ass! Gross!
by Pollonium January 19, 2014
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