Not all scars show, not all wounds heal. Sometimes you can't always see, the pain someone feels.
Just because someone is acting out in a manner that you neither like nor appreciate, doesn't mean that you have to act out in a rude manner towards them. In fact, many times it is best to treat those who treat you badly, with kindness, and with a smile. Not only are rude words killed by kind words, many people will feel compelled to change their rude attitudes to a more kind attitude, even if it only lasts for but a moment.