When you punch someone in the shoulder and at the same time yell "Fist Five"
"Dude why did you just punch me?"
"i didn't i gave you a fist five"
When you can't decide between a fist bump or a high five, you have the fist five. One person offers the five and the other fist bumps.
Or you're too cool for both, so you have a mix!
We got that just right;
person 1: offers high five
person 2: fist bumps
Yeah fist five!