Does your vampire worry about others witnessing them feeding?

All three - it depends on the vampire. My main vampire is a guilty drinker, but tries to manage his thirst with plasma packs and plasma fruit recipes. He used to feed on sims whenever he wanted, but he is trying to put his dark past behind him.

I don't think my vampire sims care one way or the other. I personally don't let them feed off of human sims because if you do it just starts an endless cycle of annoying phone activity from other sims texting all the time to tell them how bad that are and I can't deal with it.

Depends on the vampire, really.

I only have one vampire sim, and he is pure evil--he doesn't care who sees

I have one vampire in particular that wants absolute vampire domination in one save, and she WANTS the prey to see what exactly is going to happen to them.

Depends on the vampire. Old man Straud and his wife do not care. His daughters are every flavor of the rainbow. Caleb and his family do care, but to differing degrees.

I play two different vampire clans, and while the Modern clan try to live like humans sleeping at night and feeding from plasma drinks etc, the Traditional Clan (leaded by Vlad, of course) only feed from sims. They often keep prisoners to feed from, but especially when their household gets bigger, they also feed from random sims during the night. And - they don't put up a performance wanting an audience, but they don't mind if observed, either. Being seen might build them some respect, and in my game the clan controls Hollow, where they also control the residents. Nobody would dare to report a vampire attack.

On a side note, I wish those random sims walking by an ongoing feeding would react more often. Most of them hardly care at all.

I put in other.
The reason is that I have some Vampire sims that don't care, but ask for permission to drink plasma, if the answer is no, they leave the Sim alone.
Some of my Vampires will drink plasma, but get embarrassed at being caught, even it they are given permission to do so.
While my other Vampires will stalk their prey, corner them, and then drink their plasma.
Finally, I have some Vampires who don't care about being seen, and drink the plasma regardless of permission or not. The Sims they target tend to have been rude to them some way, and they are getting back at them.

It usually depends on their personality or the story. In my last decade's challenge, my vampire did not want anyone to see and if he made a mistake and was caught then the sim would disappear. In some of my modern playthroughs, they didn't mind so much due to society's take on vampirism. Being seen mostly as a personal pleasure preference.

They have the Brave, Carefree & Shameless traits. >:) :p