When just the tip of your man's petite junk happens to make a brief appearance out of the bottom of his inappropriately short shorts. See the pinky. Antonym: the brain.
Is that guywinking at me? No, but he's totally giving you the peek-a-boo.
when you take a duke in a port-a-potty and your turd is so long that it doesn't splash to the bottom but sort of "stands up" out of the pool of blue chemistry at the bottom of the john.
Man after eating all those burgers & brats while tailgating, I left a helluva peek-a-boo blue at the port-a-potty.
A guy in a porn film that just hops into a scene to drop a load & then jet.
When there's a guy in the background of a porn flick that is beating off in the shadows and his only reason for being there is to enter the main scene & drop his "product" on the girls jaw line. When that's done he vanishes. Sometimes you may ask yourself, "Where did he come from!? And why!? That was a peek-a-boo popshot if I've ever seen one!"
The result of excessive drinking and debautchalism, a brown snake peek-a-boo is that poop that everyone periodically has (even girls that think they're "hot") that refuses to play nice. Instead, it comes out part way, then retreats, then comes out part way, then retreats...and so on and so forth. Fags (i.e. Jonesy) love the brown snake peek-a-boo.
Mike: Jonesy - your mom is hot.
Jonesy: I just had the best brown snake peek-a-boo!