'Koff is short for Fuck Off. The origin of the word comes from an immature attempt at censorship. Some feel that removing the first three letters, emulating an FCC strategy to essentially chop the word down to something almost unrecognizable, detracts from the vulgarity of the word.
> Dan: Hey Kyle, why don't just get out my awesome house, I'd like to hang with my cool housemates, Aaron and Al.
> Kyle: Hey Dan, kindly 'koff.