Louisiana pearl - sex act and/or prank;
1. When a male allows only the tip and bulbus end of his penis to show while floating in murkey or swampy water.
2. Also can be done in a bath tub, but must have foamy bulbbles to hide your body.
"Hey dude, I'm going to go take the girls down to the lake and look for Louisiana pearls." Meanwhile you would have sent another one of your guy friends (preferably a virgin) down to the lake early to hide in the water. Only to have the girls find the pearl and give it a good tug.