I told a guy his light was out.

I actually do this quite often. I'll be driving behind someone, and coming to a stop, I'll notice they have a taillight out. I've been known to get out at a red light, run up to the driver stopped in front of me, and let them know a brake light isn't working.
I've never been shot doing this. I've never had anyone jump out screaming at me. Could it happen? Sure. I'm "dead" certain some nutjob packing an Uzi ith an over-inflated sense of importance could conceivably think I'm trying to hijack them, but most folks are a little more pragmatic in my experience.
I never scream at them to put their hands on the wheel, or get out of the car slowly.
And we both generally leave the situation feeling better. They, because this is a small matter that could save them a ton of money on fines, or even their life from some overzealous, trigger happy cop, and me for the simple fact of denying the powers that (shouldn't) be another opportunity to fleece the sheep.

Perhaps if our LEOs stopped treating us as the enemy, talked rather than ordered, and kept THEIR hands away from their guns, more people wouldn't panic every time the lights come on behind them, and make choices that make the cop 'fear for their  safety'.
Domestic terrorists (aka raving nutjobs) kill a couple hundred a year. We call this a tragedy. We call this inhuman. We rage against the insanity.
Cops kill TWENTY FIVE hundred every year. Because they fear for THEIR safety...