getting walked on

There's a fine line from being verbally abused and politely, but firmly, stating what the situation is (whatever you're explaining). If that's not satisfactory, and you try to rectify a situation, but they're still angry (and you've done and documented the behavior and your attempts to remedy them), then maybe they'll leave AMA. If someone is threatening, that's a different story and I take a totally different approach (like threatening to call security).

even if the person threatens to come after you physically?

I'd call security, while arming myself with other nurses and witnesses. I'd also mention that if they attempt to assault you, you will have the police come and you will file charges against them. Then talk to the charge and let him/her know what's going on, that should never be tolerated, period. Period.