A quick (often anonymous) one time sexual act with another of the same or opposite sex which ends in climax.
Dude, I can't believe that had a one off with that cop to keep from getting a ticket.
Damn, you really had a one off with that hot soccer MILF behind the beer stand?
1. To act quickly without much forethought.
2. To perform a task using as little effort as possible
Person 1: "Did you finish your report?"
Person 2: "Yeah, but I one off'd it. It's a C at best."