Always badass, not bad ass.
I would say in modern day times, it usually is a good thing.
"That motorcycle is so badass."
or "That guy is such a badass" - It is slang and it usually means "cool" or "awesome" with a lean towards powerful, violent, strong, dangerous, etc...
"Jason Statham is such a badass in Transporter"
If you have seen that movie, it might give you some context.
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