saturday night at my job

So I recently just became a customer service rep at my job. My job now is not only a cashier, but I do returns, exchanges, lottery, make keys, and answer phones. Anyway, we had 4 cashiers that night and they were all guys. This one customer came to the service desk and said "can I checkout here?" I'm like sure but its 4 registers open over there. Hes like yeah I know, but I dont feel comfortable. I said to him why not, and he said because its too many guys over there. He even suggested to talk to a manager just because it was only male cashiers that night. The worst thing about it was he was married. Therefore why are you even worried if its no female cashiers? I was so pissed ..