I Need A Prank!!!

ARGHHHHHH! I am having a sleep-over, it is 6 girls and we are all 13 or 12, i have told my friend that we r doin a prank so i will do it with her! i want something that is going to be hilarious, but realistic and funny, we will be in our bedroom all night except from having tea, what can i do? It is in a couple of weeks and it will hopefully be really good, if you know a really good prank, please tell me! THANKYOU!!!!