A sexual act. When a guy is getting his joint copped (head or jerk off), and the girl doesn't want to get the jizz on her, he waits until right before he's about to cum and then smacks her hand so she aims his dick at her face and . . . bullseye bitch!
Girl: "Don't get any on me alright?"
Guy: "Don't worry. I'm about to cum . . . oh . . . (smack) . . . bullseye bitch!!"