Racne is acne on your tits. Racne is to your boobs as Acne is to your face and Bacne is to your back.
example 1:
Girl 1: "I hear letting guys jizz on your tits gets rid of your racne."
Girl 2: "REALLY? i'm breaking out so bad, i'm definitely going to try it tonight"
example 2:
"Damn she was fine but I made her keep her shirt on cause she had nasty racne"
The act of using individual example(s) of bad behavior to demonize an entire race or ethnic group and in order to gain the support of racists and/or bigots, most often in the context of politics and stoking racial hatred of minorities for political gain.
Implying that a violent criminal like Willie Horton is representative of most Black men is just race-baiting. You can't demonize an entire race based on the crimes of one individual!