Isolating

Do you ever want to be in and out of a place, like a store, without having to greet anyone? You just want to go in, get your stuff, and get out. Am I the only one who would rather not have to make eye contact with the person behind the counter sometimes? It's called "isolating" and I think it's ok on occasion. But how do I let people know I feel that way? I think I'll make a sign that says, "Sorry. Feeling isolative today."