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1.
Someone who doesn't look fat while clothed, but secretly hides a gut
I had a locker next to that kid in gym class in high school, and trust me, he's undercover fat.

She looks hot at first, but she's just an undercover fat girl hiding beneath that sweatshirt
by RC-Cola December 20, 2005

Words related to undercover fat

closet fatty ham pork secret under cover under-cover