I also work in a retail setting, and while I understand wanting to say rude things to customers from time to time, actually doing so is downright unprofessional. If I or one of my colleagues has to deal with a rotten customer we do so professionally and then have a moan about it out of earshot of any customers. We're lucky in that management is very supportive of us when dealing with difficult customers, but in turn we're expected to be professional at all times. It's a fair deal.
Treat others how you want to be treated.
Would you help a costumer if they were whistling at you like a dog?
Honestly. I'm a human, treat me like one. Your reply was just the easy way out.