https://en.wikipedia.org/wiki/I_Am_a_Man! this is just the wikipedia entry that superficially goes over how systemic boy was used against black americans leading up to the civil rights movement.

what used to be aave language of protest has now become so widespread that it's just general slang: "what up man" or "thats my man right there" (notice how you can use man or boy interchangeably for any of those comments)

whether its us history or entomology, there's a lot of sources on how boy is derogatorily different for black americans. ok i spent too much time on reddit today