Be Direct. Draw your boundaries if you can. Let them know that there is really no place in your life for them.
Be Detached. When you have to deal with them because of a work related reason for example, prepare yourself for an encounter by knowing that their negativity has nothing to do with you. It’s all about them, and how they feel about themselves.
Be Observant. Be an objective observer. When you start to get upset, notice that, and then take some deep breaths, telling yourself, “this is a sick person, help me not to get angry.” Prayer or meditation is useful at these times.