Phrase used meaning you did not fall over. Comes from the understanding that rubber is the material on the bottom of your shoes.
Friend- Dude, you were white girl wasted last night!

Friend 2- At least I kept it rubber side down.
by hiker605 May 5, 2015
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cycling slang for 'be safe'
on your next ride be sure to keep the rubber side down!
by wiggyfish September 7, 2008
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