A "Russian High-Five" is when someone brutally elbows you in the face. Generally speaking, Russian High-Fives (also known as "Russian Fives") either break several teeth in the mouth or the nose of the receiver, and it is therefore not advisable to greet anyone you actually care about in such a manner.
John: "Ivan, let me introduce you to my girlfriend next week!"
Ivan: "Do you want me to give her a Russian High-Five?"
John: "No! No Russian Fives this time, please!"
Ivan: "Do you want me to give her a Russian High-Five?"
John: "No! No Russian Fives this time, please!"
by UnearthlyEnemy October 11, 2012