I was about to post this in the bugs section except I realized the purpose of villified factions not attacking you on site was to make room for non-violent player styles. The problem is this really takes a bite out of the immersion for characters who aren't following that route (which let's be honest is 95% of people playing this game probably).

Just to give you an example, I'm villified by the Legion and I kill two of their guys outside a cave guarding it. I walk inside the cave, and none of the legions are hostile. I walk up to the closest one, and he says to me 'When the time comes, I'm the one who's going to kill you' but his stance towards me doesn't change.

Does anyone else find this pretty stupid/immersion breaking? I can't believe that Obsidian would configure it this way just to please a niche play style. In every single fallout game if you killed a member of a faction, they'd be against you. 1 through tactics through 3. But not in FNV.

Any modders out there planning to make something like this?

I've not seen this kind of behavior myself. If I go anywhere near NCRCF I get shot on sight...

If this is indeed how any other faction works (i've only angered the powder gangers in my game so far, been staying neutral at worst) I support the idea of 'fixing' it.

Yeah I'm pretty much hunted by both the legion and NCR, so I too have never noticed this behavior. They will attempt to kill me the instant they see me.

Also have automatically hostile Legion, so I reckon you want to go back to the bug reporting idea.

I just experience the same bug out of nowhere. I'm going to report this in the PC issues section. Hopefully the OP will do the same.