It's degrading and dehumanizing to do it to anyone, yes? Specify what is explicitly racist about it. Sound it out.
You're depending on signals, context, history, and implication. I'd say it's pretty straightforward, but the problem with that is crossed signals. Could just be guys monkeying around-- being jackasses. It could be guys intending to degrade someone without intending racist intent (ex. is it not racist, or less likely to be perceived as racism, if it's a black guy doing it to another black guy? Like how black guys can drop "n****r" and not worry about a second glance unless they're on national TV?)
The key to demonstrating what is explicit means reducing the noise (i.e. subtext). An example I used earlier was blackface. There's really no other signal or indication with blackface. It's uniquely tied to that tradition. Even better are explicitly racist terms, and just as much is racial invective or threats (i.e. "Go home, blackie! Your kind are too stupid to play quarterback!")