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Acronym for Realy Big Fucking Knife, often used in but not limeted to kitchens.
Chef: look out rbfk coming through

washer: ok thanks for the heads up

bob: dude nate, wheres your car?

nate: last night a guy came up to me, pulled a rbfk and told me to get out of the car so, i did.

bob: why didn't you fight him?

nate: he had a rbfk i wasent about to fuck with him!
by NateD. March 07, 2008
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