on your hand, then ask if they wanted to join the pen15 club. it worked best if you had a bunch of people do it. then you would get them to go through the secret ceramony where you would write "pen15" in the so that it looked like you wrote "Penis" and you would point and laugh. best done with sharpie marker.
chick: Pen 15 club my ass you have penis on your hand, get the fuck away from me!
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.
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!