Johnny don't do that mucker, ditch the customers like that & go out & find some more of your decent ones. Don't let them grind you down, remember the good times/custies/laughs that you have had.
Dump them & you will feel better straight away. If the custie had said that to me I would have turned him down there & then. Your in charge of your business not him. Obviously we have to bend sometimes if it benefits us for keeping the money coming in, but always its your call not the custie's.
Your the boss, it's your decision.