More often than not, this is simply a first impression. By keeping an open mind, we can get the chance to know that person, to realize our first impression was wrong.
Once I met someone whom I found a bit strange and he kind of irritated me. Until the day I started to KNOW him. He became my best Friend. He knows me and knows when something's wrong and he's there for me.
Giving people a change to know them enriched your life.