Chris Brown -- N-Bombs & Gang Threats in Showdown with Heckler

Chris Brown was the victim, for a change, in an aggressive face-off with a heckler who got dangerously close to Chris' car, then yelled to CB ... "Is that motherfu**er bulletproof?!"

The scary incident went down outside L.A. nightclub "Playhouse" -- Chris was making a quick exit in his Lamborghini when the man ran up to the car and started yelling, "I ain't never seen a ni**er jump in a car that fast, ni**er."

The man -- who's African-American -- continued a non-stop verbal assault on Chris ... saying, "Yo, scary-ass Chris is that motherfu**er bulletproof?" That's when the tension really amps up because Chris appears to yell back at the heckler ... asking if he's bulletproof.

The man replied, "I'm a crip ni**er, hell yeah, I'm bulletproof!"

Before Chris drives away, he rolls down the window of his car ... and you can hear someone (sounds like Chris) warn the heckler, "Don't get f**ked up out here, my n**ga."

Watch the clip ... it's hard to tell if the heckler is really drunk, really angry ... or both.