A simple trick, and something of a once only event, the Pen Fifteen Club was used on every new kid at my school. Ask them if they want to join your club. Tell the new kid that all the cool kids are in the club. They will always want to join. At which time you take the industrial size permanent black marker and ask the victim to hold out their right hand. Then, very slowly, deliberately and neatly, write a huge PEN15. Because you did it on their right hand, the teacher will always see the PEN15. And the victim will not squeal.

You have 15 pens in an exciting variety of styles and hues. So do all the other members. It's a whole bunch of fun. Who WOULDN'T want to be in the Pen Fifteen club? So the uncool kid, desperate to join the gang, collects together fifteen pens in an equally exciting variety of styles and hues, and proudly presents them to the club. "Brilliant!" you tell him. "You have fifteen pens! Now you can recieve the secret Pen Fifteen club sign!" Taking the biggest, blackest, and most indelible of your collection, you then write "PEN 15" in big letters on said kids hand. Gorgeous in its simplicity, and great for fucking with the sort of kid who really DID collect scented rubbers or unusual pencil sharpeners.
(PS: I believe there is already a submission for the Pen Fifteen club somewhere in the archives. However, mine is better, and I'd be willing to go head to head with the other contributor. Good luck in the swimsuit round.)