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1.
A Russian concussion is when you splooge into someones ear while their sleeping, and tape it up. Then when they wake their equilibrium is all off quilter like they had a concussion

For added fun, you can combine the moment by shaking it all up so the person is that much more confused.

Also filling both sides earns extra point for the "double Russian concussion"
"We all laughed hysterically as the soccer team gave Sheldon a Russian concussion after he passed out in the library"
by Seven87 January 15, 2006
 
2.
the effects felt the next morning after a long night of drinking vodka.
After the party last night, I woke up feeling nauseaous and had a Russian Concussion.
by hockeystar11 January 12, 2010