Never dismiss someone for being quiet. Not everyone can put themselves out on the surface. A person can sit and be still and awkward and be burning with life and love. Sometimes they are quiet BECAUSE of that intensity. Because there is a world inside them they must attend to.
The worst people are the people who mock you for not smiling, or for mumbling, or for what you are wearing, or for being awkward, or for not being a peacock who can fan out a display of social confidence on demand. Never forget these people.