In most states, you may threaten or use lethal force if you or other innocent life are in imminent danger of death or grievous bodily harm. The fine print: imminence must be imminent (the bad guy or guys must be in the act of threatening you) and the threat must be credible (a bad guy waving a knife from across the street won’t cut it, so to speak). Ultimately, it comes down to the “reasonable person standard.” Would a reasonable person think your actions were reasonable – given the totality of circumstances. Google and read your state’s “deadly force statute.” Meanwhile, know this: real life isn’t as cut-and-dried as it appears in the video above . . .
What if the guy leaning against your car was outside a strip club at 3am and you were a stripper and the guy had been hassling you all night and you knew him to be an ex-con who’s done time for felonious assault? You still couldn’t pull your gun until the above criteria were met, BUT – you might be able to do so legally if he approached you menacingly even if he wasn’t flashing a gat.
Again, imminent threat, totality of circumstances, reasonable person standard. One more thing: I wouldn’t use such a confrontational tone with Mr. Car Leaner or [necessarily] go into gunfight mode if he simply flashed his gat. That would depend on . . . you guessed it . . . the totality of circumstances.