What is Frat Mattress?
1.
1. Adjective. Loose person.
2. Female who sleeps with lots of men, usually members of a fraternity.
Laura is a big frat mattress.
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2.
Someone who gets around, and often sleeps with members of a fraternity.
Person #1: Let's do some word association. Frat Mattress.
Person #2: Whitney
Person #1: Why?
Person #2: Because it just seems to fit.
or
Whitney is such a frat mattress.
See