Well, consider this one of the most obviously stupid things you've encountered recently. In 2011, four supervisors at the West Kern Water District decided to stage a mock robbery in their work place. Following a training on responding to robberies, the supervisors snuck out of the office, with one soon returning dressed in a ski mask, demanding the office's money, and claiming to have a gun.
Of course, the "mock" victim hadn't been informed of the scheme beforehand. To her, everything appeared very, very real.