bad sort, a

An aggressive, mean-spirited, dangerous, or generally unpleasant person. I wouldn't get involved with him, he's known to be a bad sort. If your so-called "friend" is encouraging you to shoplift, well, then they're a bad sort. That George fellow is a bad sort. I heard he was arrested just last year for robbing a convenience store for drug money.

An unpleasant, mean person, as in We cautioned Bill about his friend, who was clearly a bad sort. The antonym is a good sort, a pleasant, kind person, as in She's a good sort, always helping her neighbors. The latter is stronger than not a bad sort, as in He seems ill-tempered now and then, but he's not a bad sort. All three terms use a sort in the sense of "kind of person." [Second half of 1800s]