[Pyro7480]

And in a school environment, aren't there specific rules against wearing clothing that may incite violence?

The precedent is against them. Tinker v. Des Moines, which was decided in 1969, stated that protest expressed through clothing (the article of clothing in the case was a black armband against the Vietnam War, which got the kid wearing it suspended) is protected by the First Amendment.

[FauxBlonde]

So if another student wanted to wear a shirt that said James Nixon is a Hateful Jackass, that would be no problem?