Globalisation and all, word etymology can be an interesting phenomenon at times.
The Brits in India during the time of the Raj (colonial times), had encountered a practice known as thagi. This was in no way representative for Indians nor was it a widespread "phenomenon" yet the Brits used the occurence of thagi in their campaign to stress the difference between themselves and their Indian subjects in order to justify a need to stay on and "civilize" a nation they sought out to declare uncivilized at all costs*.
The thags were a group of people who worshipped the goddess Kali and they would steal from and strangle their victims, as a sort of offering. Thus during the 19th century in Britain a thug came to be knows as a particularly nasty kind of ruffian.
From 19th century Britain to 21st century Brooklyn, where one is "positively" self-declared as a "thug for life". Ironic.
*Ideologies of the Raj by Thomas R. Metcalf