Dealing with rude customers is one of the worst things about working retail, because you have to handle their anger and bad attitude without blowing up in their face or being rude back if you want to keep your job.
And while it is extremely satisfying to tell a customer where they can stuff their opinion then quit the job on the spot most people can't go out in a blaze of glory because they need to pay their rent.
So instead of storming out you should do like the retail worker does in this comic strip by AC Stuart and come up with clever yet snide responses to the stupid and rude things customers will inevitably say to you.
But whatever you do don't show customers any fear...they feed on that stuff...
See 8 Perfect Responses For Rude Customers here (NSFW language)