An old grade school prank. You'd write Pen 14 on your hand and walk up to an unsuspecting schoolmate and ask him if he wanted to join telling him he could be Pen 15. You'd then write Pen 15 on his hand, and everyone would laugh at him.
"I'm in the Pen club. I'm Pen 14, you can be Pen 15."
by Ritley August 25, 2003
or Pen15. Resembles the word "penis" when written.
by webstersheir62 March 1, 2003
A club that unlocks the secrets of the universe.
“To join the ‘pen 15 club’ just write it on your wrist in sharpie”
pen 15 is slang for penisalso see cock wang and dick
by purplemonky November 12, 2003
Something your friends tell you to write on your arm. They Call it A "CLUB".

Its NOT!!!!!
Guy:JOIN Pen 15

Me:..... OK!!!!!

*Writes Pen15*

by Ninoots! March 25, 2014
Someone might ask you to join their pen club, but they already have 14 members so you can become 'pen 15'. They will write this on your arm so it will be defined who you are! Never turn down someone who asks you to your pen club
"hey wanna join my pen club? youcan be 'Pen 15'!"
by Vinny Eoh April 11, 2019