It's a multi-meaning thing. On the lighter side, of course it is from Who Put th' Bomp? and "...Let's go racing!" And it's a downshift thing when someone thinks he'll pass on my right and take the space I'm driving in. (Though just yesterday I had to back off and let an idiot in a Jeep in so he wouldn't hit the car in front of him) On the darker side, it's a reflexive, self-defence thing. Ask the guy who swung a jack handle at me twice when I was 16. I got tired of blocking it with my forearm. Ask the burglar that pulled a knife in the dark. But you may not have guessed that it is from my years with an international Irish dance troupe.