Top Definition
A person that attempts to have sex with as many women as possible, while, at the same time, trying to keep it a secret from each woman. In his head O.S thinks that the illusion will last, however, that is not the case. Often most of these women know each other. If your friend is an O.S, best thing to do is let it take its course. Then when the shit hits the fan, kick back, pop open a cold one and enjoy the show.
Bob-"Hey whats up O.S?"
British Simon -" O.S? Operating system?"
Bob-" Nah. Operation scumbag."
by KBap April 27, 2011

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