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From Mario Kart, a Nintendo game.

Whenever you get ahead and think you have it made, someone behind you shoots a blue shell at you and takes you out.

(Blue shells fly directly to the person in first place and pack the biggest punch in the game)
I was doing great at my new job then I was blue shelled. (fired)
by Toadster March 10, 2004
When a guy and a girl are having sex and the girl thinks the guy is going to finish too early, she smacks him hard on the balls so that she can finish first.
Sam: I was so close to finishing last night with Diane but then she totally blue shelled me and now I'm walking funny.
by Pow! Right in the kisser! December 13, 2010