I've always found that intoxicated patients react to the way you present yourself in a situation. I'm small (5'3" and 125#), so I know that while I'm a scrappy fighter, I do not want to have to tussle with any patients. I always present myself in a professional manner, act sweet as pie, and ALWAYS end up with the patient wrapped around my finger. That being said, I don't give my patients an inch. If they are being disrespectful, I let them know, but in my most respectful way possible.
As for the focused/trauma assesment, unless you have an x-ray machine, a CT scanner, and an MRI, the assume the worst. Who knows, maybe your patient fell off of his stool because he's nursing a stab wound between the ribs up at his arm pit. Or maybe he was just a sloppy drunk. But either way, and ESPECIALLY because you're dealing with a geriatric pt, you should always cover your butt and the bases. It really is better to do too much than not enough in our line of work.