When he/she is sleeping get toys/stuffed animals etc into a circle around your friend, Next start screaming OH MY GOD THEIR ALIVE!!!!!!!!!!!!!!!!!!!!!!And if your friend is very dumb they will buy it. Also it would help to start crying.
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do something funny
pull a prank on him
Trick them into making their own head explode.
You can view videos of the skirt pull prank and learn how to perform it from the videos at the YouTube website. Once on the website, type "Skirt pull prank" into the search field at the top of the page and press enter to bring up the information.
they drew on his face
Peter put a dead mouse on Mr. Dussel's bed as a prank.
A fart machine in there desk
Give someone a swirly or wedgie
Put gum in his hair
That depends if you want to get into trouble or not.
Whoopie Cushion is always a classic!