Take some cookies and sit in the middle of the floor and eat them. If somebody asks you if you payed for them say "You have to actually PAY????"
Open a Skittles bag, throw them at people, and yell "TASTE THE RAINBOW!!" ((XD I am gonna do that at school on tuesday))
Do you like Naruto? Pretend to be Itachi! (zomg i started collecting the cards. I've got dead smexy sasuke and this guy named dan i dont know who he is)
Start singing the Potter Puppet Pals songs from the Live one and from TMTN (The Mysterious Ticking Noise)
Ask where they stock the avatars.
Take an item from the store, bring it to the check out place and demand ur money back.
Fill a boys cart with girl stuff (pads, tampons, bras, thongs, bikinis, barbies, bratz etc.) and girls cart with boy stuff (boy underwear, boy junk etc.)