The proper response to either a high-five or a knuckle-bump is to go ahead and perform the action, but then follow it up with an enthusiastic “Head butt!”.
The number of high-fives and knuckle-bumps offered will decline dramatically.
“HIGH FIVE!”
[point at your shoulder and shrug]
“Sorry, torn rotator cuff.”
[look sad and walk away]
Yea, I was all ready to post an opposing point of view. What the heck, I’m posting it anyway. 