Well in your social and personal life we need to avoid such people.  If not we are destined to be pulled down emotionally by such negative exposure.  You have a right to be happy.  Therefore, it is important to eliminate negative people from your life.  Now on the other hand; we do need to learn how to deal with difficult people.  Especially in places were we can’t avoid these negative personalities (like work).  My suggestion is smile, be kind and remember you don’t have to extend the relationship pass what is required.