Ermm... I have been killed in NCR.
I just died, and I didn't attack anyone for a long time, I didn't even get message "You did troubles, so guards won't protect you." I didn't steal, I didn't attack anyone (even thieves or other unportected).
One guy called Ablul punched me for fun, and guards ignored it, then other 2-3 guys started to punch me, and punched me to death.
So, what a reason? Why?
Edit:
Also, if you attack ANYONE in town, whoever it is, thief, unprotected guy, or just idiot, you'll become unprotected too. So be careful of attacking thieves.
Guards said:
"<Name>, seems like Boli is interested in your possesions." like 100 times.
I said to him "die", and then shot his head, but guards killed me. He have uber-mega-super-puper-Idolized reputation at NCR?
Ok, guard said it not 100 times, but more than 10 100%, because I was watching how he robs people for a long time, and then I couldn't resist to shot him.
Guards' behavior is random and crazy, they do whatever they want, sometimes they shoot, sometimes not, sometimes protect, sometimes not.
Now I understand what it was... he wasn't stealing, he was planting dynamite.