One of my favorites is to go into somebody's room and turn EVERYTHING upside down.

One of my favorites is to go into somebody's room and turn EVERYTHING upside
down. This was done to the cook at a summer camp I worked at (she was a lousy
cook; this was revenge for hamburger in white sauce for breakfast). We invertedeverything in the kitchen; the stove, the refrigerator (both previously
disconnected) and everything in the refrigerator; everything on the shelves and which (i.e., top, bottom, middle) shelf it was on. Best of all, there was a
table in the middle of the room with large JARS of ketchup, mustard, etc.; the
tops of all of these were hidden and they were inverted (place waxed paper over
mouth of jar, invert, remove paper) and the table rested on top. We also
inverted several posters on the walls.
Of course, the cook wasn't very happy about this; after she'd gotten it cleaned
up she demanded that whever did it apologize and wash dishes for a week. If
nobody claimed responsibility, she said, she would quit.
We cheered.