I used to work for place where we had a night shift, not just cleaners but actual employees who worked all night. A woman I worked with noticed odd things about her desk, like somebody had been using her computer at night. She looked around and discovered a new folder created by one of the night time workers, with subfolders. One subfolder full of porn, the other with various drafts of his CV and cover letters.
We decided to play a prank, and made up a fake email from the FBI listing the sites he visited and detailing the investigation and telling him to report to the US Embassy at a certain time for questioning. We also said in the letter that other people would be called in for questioning, and listed some of his old professors and former employers he had listed as references.
We actually sent the email, but then a few minutes later we started to worry that the guy might kill himself or do something crazy so we sent him another one saying it was just a joke. At least he stayed out of our office after that.
