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1 definition by Chaosweaver

 
1.
A law of physics generally attributed to Anime, in which breasts move independent of gravity and jiggle absurdly with even the smallest motion.
"Dude, did you see that chick?" "Yeah, she was Gainaxing so bad, I thought she'd get a black eye."

"I would run more often, but not even my sports bra can stop the gainaxing. it really hurts my back."
by Chaosweaver November 01, 2012