Simple, annoying and low-tech: Take the top 5, or so, styrofoam cups off the top of the stack next to the coffee pot and poke several small holes in the bottom of it with a pin. Then poke several larger holes in the next one down. Replace cups onto stack. Wait for amusement. :thumbs:
When someone pours coffee into the first somewhat leaky cup, they will usually grab the next one and dump their coffee into it. Much hilarity ensues as leaking gets far worse! :cool: