What is Fart Fan?
1.
n.
1. the ventilating fan in the restroom that you turn on while you
"make sure to turn on the fart fan when you're in there!"
2.
A practical joke in which the trickster places a fan, typically oscillating, near the person to be tricked. The trickster then walks by and farts into the fan thus blowing a not so fresh breeze of ass stink all over the victim.
When your mother comes over we'll have to give her a fart fan.
See