I'm surprised that so many people would be capable of controlling their instant-reaction facial expressions. I would certainly try not to make a scene if something shocked me but I guarantee you it's going to read on my face for a moment before I'm able to compose myself. Just how long a moment depends on the person and whatever it was they've seen, we all have different thresholds for what shocks us. If someone happens to be looking at me when that expression crosses my face, gets angry and yells at me, that makes the interaction my fault? I just don't get that logic at all.
We can't walk through life like robots. I think I have a reasonable expectation that I won't see nudity in the grocery store, and someone else should have a reasonable expectation that, if they choose to be partially nude in public, some people aren't going to enjoy it. If they want to rant, rave and curse because they could tell I internally went "eww!" for a second I think that's 100% their problem. I'm not going to be held accountable for unleashing someone's crazy by having a normal human reaction, especially if it only lasts a few seconds and I move away.