I think it is, and I am also guilty of this. There are times when I will distance myself to people just because how they present themselves isn't the kind that brings a pleasant feeling. Personally, I don't think of this as a huge offense, but not that it is a good practice either. Perhaps this is just the initial human response to something we don't know, especially when it's emitting a bad feeling that we perceive may harm us? I am not quite sure either. But we, as the humans that we are, care so much for ourselves that we don't to be caught off guard or be hurt by our own carelessness. What would make this response unacceptable, is if we are to act to that vibe even if the other person's not doing anything against us.