A club in most middle schools around the country. Consisting of mostly prepubescent boys.
Each member receives a "club card" with their name and "Pen15 Club Member" on the card.
When the new member receives the club card then realizes that he/she has just joined the penis club.
Joe: Billy do you want to join the Pen Fifteen Club?
Billy: YES! I will conform to you all because I want to be cool and popular!
Joe (while snickering): Here is your membership card!
Billy: You wrote Pen15 Club! that is the same as the Penis Club! HAHA, OMFG, LMAFO, LOLZ!