Bad Impressions?

Sometimes it's difficult to know what people are thinking. It's so simple to drive people away with a single sentence, or a vague vibe that they pick up. I wonder if it's worthwhile to bother with such people. On one hand, they're clearly not making an effort to get to know me better. On the other hand, they probably have reason to be this wary. I really don't know, 'coz I hate to get people turned off, yet I do not want to associate with people whose perceptions can hinge on a single impression.