Is your accent much different from the people's in this CVS? The store clerk might have responded the way he did because of not hearing your question clearly?

Do you resemble a celebrity? That would cause people to stare while they are trying to figure out who you are. Do you think it is some kind of racial discrimination?

Was it actually too cold for shorts? People sometimes stare at others when they seem oddly dressed for the weather.

I read that one of the ways stores can deter theft is to greet the customers as they come in. They do that at the drugstore I frequent. Sometimes I can't even see who is greeting me because of displays, etc. It must be working--I haven't stolen anything

If that had happened to me, I'd go in again and if they still acted strangely I'd probably say something like "I'm surprised you're not friendlier, given the economy."