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a day in which a person (most often a teenage girl) wears sweatpants, with her hair up, and no make up. these days are most common after a late night, a break up, or paired with a hangover.
it is best to not mess with a girl on these days, she will attack.
Oh no! She's wearing sweat pants. It must be a sweatpants day! Don't mess with her.
by anonnnnnnnonon January 15, 2011
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