A vicious, violent piece of sh*t scumbag who deserves a good kicking. Lately has come to mean a self-pitying piece of sh*t scumbag who deserves a good kicking.
The reason you should never give someone like this an even break is because they wouldn't cut you any slack either. A thug is not, as wanksta rappers would make out, an innocent suviving in a tough world; a thug is a merciless, violent criminal who beats and kills for fun. It is not a state of being for anyone to aspire to.
Origins: The word "thug" originally refers to members of a Hindu cult forming part of the (South Asian) Indian criminal underclass; it is similar to Satanism only more violent. Also see Santa Muerte