I'll try to have more than one idea. Useless Powers Day: Has your character ever wanted to have a super power? On this day characters wake up with a super power. Too bad that it's a stupid, and or useless power. The ability to type at 60 words per second. The ability to stare at someone without blinking. The amazing power to completely ignore annoying people. ETC ETC.
Cartoon Day: On this day characters wake up as animated characters in a typical animated world. Reality is in the eye of the beholder. How will your character handle being 2D for a day?