a person who exists by criminal activities or has a way of life that most people disapprove of

There are plenty of lowlifes out there, ready to take advantage of unsuspecting senior citizens. 到处都有许多卑劣的人，随时打算占没防备的老人的便宜。

the group of people who exist by criminal activities or have a way of life that most people disapprove of

He started mixing with drug dealers, pimps, and other lowlife. 他开始与毒贩、皮条客等不法之徒混在一起。