流氓 (liú máng): rogue; hoodlum; gangster; immoral behavior

Late at night in an alley, a few thugs stopped her and snatched her wallet.

He borrows money but never repays it, and even threatens his creditors—he's simply a rogue.

Police patrol near the train station, specifically cracking down on gangs of thugs.

That hooligan was harassing a girl on the street and was stopped by passersby who called the police.

Kids, don't associate with those rogues; they'll lead you astray.