Buy a chocolate bar, then go into the bathroom with it, and go in a stall. Eat it, and then smear some from the wrapper over the stall door, wall, floor, toilet seat, and melt some more choco on the toilet paper dispenser.
c: leave the stall (Hide the wrapper in a bag or towel of course) and have a piece of toilet paper stuck to your shoe, and have chocolate completely smeared all over it
Get access with the intercom and say "Jump up kick back whip around and spin! And then we jump back, do it again!" and then get friends on the intercom to say "Ninja! Go! Ninja! Go!"
Walk up to someone and just smile, and then follow them around, with a creepy smile until they do something. If they speak, respond with clucks and peeps.
Wait until the store is busy and people are constantly coming in and out of the doors. Walk through the door, and instead of holding it open for the next person, slam it in their face and shout "YOU'RE NOT ALLOWED IN THE CLUB!"