The most common rendering is the word "salaud" ([salo]). It is also used as an insult.
(TLFi) B. 1. Surtout au masc., arg., pop., injurieux. Personne méprisable, dénuée de toute moralité; personne capable d'actes contraires à tous les principes moraux.
There is a much more vulgar term, "fumier" ([fymje]), (also used as an insult).
(TLFi) 2. Vulg. [Terme d'injure] Personne qui ne mérite que du mépris. Synon. ordure, salaud.
The following terms from standard French are not vulgar but they have lost their force and are not used any more.
- canaille ((TLFi) B. Usuel. [Désigne des individus] Individu malhonnête et sans scrupules.)
To be consistent, considering that "bad man" is not slang but standard English, a word like "canaille" would be better. It's a word we still find in a song by Gainsbourg, so it is not that much "out of fashion".
There are words that have less general connotations of badness and refer to men specifically involved in illegal activity.
- malfrat ((TLFi) Arg. et pop. Malfaiteur, voyou.)
"Glauque" is not used in standard French to say "bad", except in a restricted part of the population, that is to say certain people such as those that like pornography; you find the term "femme glauque"; that is a name for a woman doing pornographic shows.