Mine has taken to closing the ( normally open) sliding glass door and polishing the glass. I've been caught about 3 times in the last 18 months and it bloody hurts!
That sounds kind of like a prank we pulled on our (female, and able to take a joke) boss; we Saran-Wrapped the toilet bowl.
Of course, her husband didn't find it nearly as fully when he pissed into the Sarah Wrap at 5:00 AM and had to clean it up.