When you're at a party and a female is rubbing on you in a passionate way. After a while, you sit down with her and some buddies and she's sitting next to you giving you a hard on. You get up to get some punch, but you have to squeeze through some chairs with some
people sitting on them. You squeeze through accidentally slapping someone in the
face with your
boner and run away fearing to look back.
See also johnson slap