The Impossible Paper Illusion is a staple of the surprisingly vast canon of paper tricks. With scissors and paper as the only supplies, three strategically placed slits can make a trippy magic flap. The surprisingly lucid HowToLifeHacks420 posted a tutorial of the gimmick, and even though they still call the illusion "impossible," now you can see how it's done. (Although, you might have to watch it a few times to get it.)
With the flip, the flap can't fit into the vacant spots.
For more fun with office supplies, check out this video of ten paper tricks that over 22 million people have gotten into.
If you want to quickly and easily confuse someone at work, take a tip from Beyoncé: your best revenge is your paper.