My best prank would be to tie a bunch of helium balloons to a chair and tie a really long rope to the chair (probably 20 feet high). Then tell someone the skit will be for them to get in the chair and the balloons will take them up and they won't know how to get down. Once they are up in the air and have no way to get down then you can throw things at them... like poop. And to top it off you could shoot paint ball guns at the balloons to pop them and let the person down.
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