Is the word used more often in reference to blacks (or other minorities) implicated in crimes, in a literal or metaphorical sense? Quite possibly. Has it sometimes been used with undertones of racial hostility? No doubt—though the same could be said of any other negative epithet. But to suggest that it is not used in reference to white people is absurd. Even many commenters on the left-wing Daily Kos website were skeptical when the claim that “thug” is an anti-black slur popped up in a blogpost last October. The blogger was clearly oblivious to the fact that the Daily Kos’s preferred anti-Republican slur is “rethug”—it even has its own tag.
For what it’s worth, I’ve found some right-wing Internet users’ in-your-face insistence on describing Michael Brown and Trayvon Martin as “thugs” distasteful and cringeworthy; whatever their offenses (which, at least for Martin, remain in the realm of speculation), these are two tragically dead teenagers. I also agree that we should be using the “T-word” more often to describe police officers who abuse their power and brutalize the people they are sworn to protect. But none of that means it’s an inappropriate word for rioters.
Which brings us to the other specious claim: that “riot” is a racially biased term.