This white boy makes it abundantly clear that there are vocally racist students at Bri's school. In particular, though nothing physical happens here, this can be read as an implicit threat of violence—or at the very least, that this boy expects that at some point, the black students will be "put in their place." This reminds the reader that school isn't a safe place for Bri or the other black students. They constantly have to be on guard for things like this that might compromise their safety or get them into trouble.