1. A phrase used as a formal declaration of defeat. For example: "Kenneth replied 'yo mama' when he realized he could not counter his opponent's point."\r
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2. The principle part of a "Yo Mama" joke, usually entailing a description of your mother being so "something" that "something" occurred as a result.
> 1. Amy: You're so ugly!
> Gwen: Yeah, well so's YO MAMA!
> 2. "Yo mama so fat, the last time she saw 90210 was on a scale!"
> "Yo mama so dumb, she thought a quarterback was a refund."