Meaning
A tough, fearless man — and, depending on tone, either a genuine gangster figure to be feared or, in the flip so common in Patois, simply someone admirable, skilled, and not to be messed with. Here 'bad' often means good: a 'bad man' at a thing is formidable and impressive, a 'baddest' player commands real respect. So the word runs from the dangerous gunman of the streets to the man who is simply excellent and untouchable, and only the tone and context tell which kind of 'bad man' is meant.
Examples
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Nuh test him, him a real bad man.
Don't test him, he's genuinely dangerous.
-
Yuh a bad man pon di football field!
You're a beast on the football field!
Here 'bad man' is pure praise for skill.
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Bad man nuh dweet so.
A real tough guy doesn't act like that.
Origin
From English 'bad man', but shaped by the Patois habit of using 'bad' to mean excellent or formidable, so the sense swings between menace and admiration.
How it’s used
Tone and context decide whether it is a warning or a compliment. A recurring persona in dancehall lyrics.