I did the mildest of pranks -- installed somewifi-controlled colored lights in our house and surprised Mr. Mico when he went to the bathroom with a light show. He loved it.
I also introduced my coworkers to the Chrome extension "cloud-to-butt" which replaces all text occurences of "cloud" with "butt." Our company uses the word "cloud" ALL OVER its website, so it was extra hilarious.
At my office, we have visitor parking signs in some of the spots close to the entrance. Someone at my office replaced one of those signs with a sign for their boss and some inside joke about him that I didn't get. I was mostly impressed because they had a custom metal sign made to replace the other one. So that took effort.
I saw someone else announce on facebook that they had accepted a new job with InGen. They linked to the fake InGen website so all of the "related pages" that showed up below their post were about jurassic park. And a few people posted some pretty clever "congrats" responses that referenced dinosaurs and the movies/books. People still bought it.
