I have a customer who is just a total a****ole to me.  I can be s polite as could be to her and be professional as possible and she b***hes through every step of the  conversation.  Moans about every detail.  Chews me out to the mangers each time she comes through about the tiniest detail.  Last time I asked her for her QFC card she threw her car keys at me.  It's gotten to the point of I won't say a single word to her during her entire session with her.  She still finds little details to harass to the managers about me.  The managers are aware of the situation. 

I was going to the next step:  Tell her as politely as I can "I'm sorry if my best offends you but I'm calling another cashier and you're just going to have to wait." 

The problem about this is "The customer is always right."  The mangers enforce it.  Her lies have gotten me written up a few times.  I am uncomfortable around her due to how she treats me:  She is harassive, abusive and an a**hole towards me.  Should I begin denying her service for the way she is treating me? 

She is elderly and obviously uses that to her trump card.  I have a mild disability that is also to a mild degree mental.  I asked a lawyer along time ago regarding another issue and they stated that mental issues always win over physical unless they individual is physically paralyzed.