Maybe you looked like you knew just what you needed and they saw you and didn't want to bother you. Yeah they could have asked you if you found everything ok while you were looking on a shelf etc but I don't think a lot of stores do that unless the customer looks confused about finding something.

Do you mean "utter" rudeness where you wrote "uber"?

When I go into a store and need help, I either ask someone if I need help, or someone sees my confusion and asks me, but only if they are not busy and involved. But many times I want to be left alone. Thats just me and I see that is not you. I don't always want to interact, because sometimes too much help feels like you are walking throught the perfume dept. and all sprayers are ready for you! LOL You just want to grab the item and go. So maybe they were giving you space.

While your letter mentions how you were insulted, it doesn't go into more specific details that would convince me they were deliberately rude though. Yes the register person could have said that, but many places don't or only do that on occasion. It is a nice perk if it does happen.