Actually, my father would disagree.. Hospitals are excellent places for pranks, provided you know the limits. The urine sample / apple juice switcheroo should only be done in *one* direction, for example.
One thing my father would do was what he referred to as ‘The Bedpan Trick’. Not so much of a prank, really, but still ingenious. Doctors and surgeons had lunch in the cafeteria. Often, they would not finish everything they had collected from the cafeteria, particularly if they were on call. As such, there would be wrapped sandwiches, fruit bowls, cartons of milk, and even pie that had not been touched. My father - or one of his Physical Therapy buddies - would slip in before the table could be cleared, with a fresh, sterilized bedpan, and load it up with the bounty of goodies. They would then toss a towel over it, and head on down to the PT department for a snack.
This worked rather well, because nobody in a hospital is going to ask what’s in a bedpan with a towel over it, even if you’re walking out of the cafeteria with it.