Abreviation for "Full of Shit"
You are so "F.O.S."
They are really so "F.O.S."
by Bev Lane May 29, 2006
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Code word for full of shit to get you out of trouble. You say it to someone and they just look confused when other people might realize what it means. Can also be pronounced Fos for short.
When my teacher told me that my homework assignment I turned in was worth a D when I knew it was worth and A, I said "You're F.O.S., this work is flawless!" I got sent to the office because apparently he knew what F.O.S. meant.
by PrincessR December 06, 2009
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Acronym for Fuck On Sight. A type of individual when seen by another, one would be willing to have sex with without knowing anything about them, not even their name.
"Dude, that girl in the parking lot, her eyes, those hips, she's a definite F.O.S."
by mayej May 10, 2009
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Short for "Full Of Shitness"

A serious condition in which a person chooses a malady to be a victim of. This malady is usually vague, chronic and untreatable such as a "bad knee."

F.O.S. will tend to flare up when the person is confronted with a situation they would rather avoid.
"Is Robbie coming to your birthday party today?"

"No, she texted me yesterday. Apparently her F.O.S. is acting up, making it impossible for her to walk on her bad knee."
by mizJD January 10, 2010
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Full Of Shit: no data, no proof, a baseless opinion.
He's F.O.S. He doesn't know what he's talking about.
by gmerritt November 07, 2005
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