In college, we had heaters in our dorms, metal units under the windows with panel covers that came off. One afternoon, we picked the lock of a really annoying kid's room. One of the guys went in, removed said panel, sat a carton of milk in there, and replaced the panel. The door was then closed and locked...and Dissonance countered with one about a flying watermelon, complete with cardbord stabilizer fins. Since there's not much else to discuss right now, uhm, maybe you all would like to share your own stories in the comments?
A month or more later, there was a pretty big ruckus down the hall, and when the room's occupants finally threw the milk out of the window, it stunk up the whole dorm area for a day or two. Outdoors.
OMG, their room had to have a building funk for weeks before they figured it out. It was RIPE by the time they finally went so far as to pull off that heater panel.