The act of a man capping off an orgasm with a thumb, for 2 or 3 seconds, then releasing the pressurized coom. The captain part is if the ropes are more than 3.
Hey bud, did you bring home the slampig from the bar? You think you’re going to pull a captain cap off?
guy 1: Hey man do you see that hot girl over there? guy 2: I sure do. She's so fine. guy 1: I'm gonna get her to cap me off later. guy 2: Good luck bro.