Commonly used by medical or surgical residents.
I don't want to operate on that guy, he's a high-fiver.
A young man would be doing his female partner doggie-style while his friend would be receiving oral sex from the very same girl. In this process, both men would be giving each other high fives over the girl's head.
As I was fornicating with my new lover, my friend joined in by shoving his erect cock into her mouth. My friend and I engaged in an exchange of high-fivers while we were getting busy with her.