How to answer
When you come to work, you are there to work. Not be in constant arguments with fellow employees. Unless you are an executive and making a high level decision, your argument with a fellow coworker is not that important. Specifically in a retail setting where customers are always around. Now, this question could also relate to your engagement with customers. Just ask yourself, Why in the world would you ever get into an argument with a customer? Customer is always right, you are there to serve the customer and help them with their project. If Customer would like to rip off every roof shingle with a putty knife, who are you to tell them otherwise? Sure, tell them that would be a long painstaking process and they should at least consider the claw on a hammer, if they are unwilling to spend money on a shingle remover. With that said, tell the interviewer this job is not about your pride, but about helping customers, and your only concern is that they leave happy and with any knowledge you may provide. If they reject it, so be it.