From time to time, I will accuse someone of being a thug. This is not just a term of general disapproval with criminal implications. The original thugs, or thuggee, were members of a cult in India in the 1830s, devoted to the goddess Kali, which is believed to have murdered in excess of 30,000 people, mostly travelers. The modus operandi of the thugs was to join a caravan, a few at a time, accompanied by their wives and children, and blend in with the other travelers. Then, when a critical mass of thugs was present, they would turn on their fellow travelers, slaughter them all, and make off with their trade goods and possessions.
So when I use the term, I think of someone who passes as just another citizen, but who has a hidden agenda that may not be as immediately lethal as the original thugs, but who is dangerous to my (and everyone else’s) life and wealth.