So this might not be advice, but maybe the opposite, but c'mon. This prank has to make you smile. :)
What you need:
And of course, an Oreo
First, open the Oreo, so that there's cream on one side and just the cookie on the other. Then, scrape the cream from the cookie with the butter knife, so only the cookie remains. (Make sure to eat the cream, though! XD) Then, squeeze a bit of white toothpaste on the cookie and spread it with the knife. Finally, put the other cookie on top of the 'cream' and then serve. Await the reaction and then RUN!
Awesome prank that ANYONE can do! :D