A liquid bonus, typically a six-pack of the performer's choice, attached to an action, and granted after completion of the action. The action is typically crude in nature, such as having sex with someone for situational humor, or finishing a large quantity of alcohol.
Bob, Ted, Fred and Jimmy are at a bar:
Bob: "So my sister and mother are coming to visit next week"
Ted: "Beverage Incentive!"
A week later, after Jimmy successfully slays both:
Ted: "Jimmy, here's your two six packs. I'm going to put down another beverage incentive. If you finish all 12 beers in 20 minutes, I'll get you another six pack"