Does not qualify as a rude customer story, but I had this happen recently at a home improvement store I stopped at. As I was approaching the entrance in, a friend of mine, who works at the store, and one of his co-workers were coming out pushing a pallet jack of laminate flooring. I stopped to chat with them, and as we were chatting, some guy pulled up in his p/u truck, jumped out, and showed them his receipt. My firend and his co-worker began to load the flooring in the guys truck.
The guy was watching them, then turned to me , and said "are you just going to stand there, or are you going to help load my truck?" I replied that if he had asked nicely, I would have helped him, but since you acted like a prick, I'll just watch. He then replied "Who do you think you are?" I'll go inside and report you to the manager!" I replied, I'll do you one better, and walk you in by the hand asshole, and we'll look for the manager together.
By that time, my friend and his co-worker, who had both stopped loading the guys truck, were watching and listening to the exchange. My friend then leaned over and told the guy that I did not work there. I said to the guy "bet you feel like a bigger dickhead than you appear to be." He put his head down, helped load the truck, and drove away without saying another word, or looking up.