I think that there are some people (not on this forum) who use the word thug primarily when talking about inner city blacks hence the inference that they're really just using it as a stand-in for the word 'nigger'. Then when called on it they claim you're the PC police.
Then there are people who use the term thug without a strict racial connotation and apply it to anyone who acts thug-like. When they get called out by someone implying that they are actually racist they also pull the PC police card, but they're probably right in some regards in that instance.