Someone who is crazy, or acting crazily.
"Look how recklessly that man is driving. (he is a) madbrain"
by bananamilkshakefiend October 15, 2009
1 more definition
Mad Brains is a synonym for the incidence of receiving a very good blow job.
Man, that girl gave me mad brains last night.
by pba24899 February 20, 2010