When dealing with an abusive client, the most important thing to remember is that you are not their therapist, their personal shopper, or their mother.
Do not, I repeat, DO NOT, try to reason with them. They will not listen, and you will end up wondering why you ever got into this line of work.
Also, please do not, under any circumstances, try to explain the concept of empathy to them. Trust me, they won't get it.