Picric acid, huh. When I was a grad student and the Head TA, we had a really obnoxious colleague, just a real PIA. So....... before his lab section we went and put a very, very thin layer on most of the surfaces he would touch first. Lots of little pops and bangs and the roars of us laughing. No harm to them, but they never, never tried to mess with the rest of us again. Now, I would probably be suspended and arrested! Then, a harmless prank to teach them a lesson.
Mike