The term "piece of ass" has the primary meaning of a sexually attractive person. When someone is looking for it, that means that they are looking for someone to have sex with. If they say they got it, that means they had sex. Here we have one that is described as jailbait and black. Black is obviously referring to the skin color and jailbait to the age. If you first consider the word jailbait itself, you probably recognize both jail and bait. So this would be a bait (like that for fish) that can get you in jail. It's a temptation that can get you in legal trouble. Having sex with a person under 18 years of age in the US is considered statutory rape and will get you many years of prison time. So this could be also referred to as a "very young and sexy African-American girl" or something along those lines.

Good lord! Yes please don't repeat this!!

Terry, it's okay for a novelist to create vulgar dialogue to reflect reality. It would not be acceptable for you to speak or write like that.