Helping A Customer To Help Themself

A customer walks up to the register across from mine, which is closed. My current customer is speaking to me, and I can’t interrupt, so it takes around ten seconds before I can say to the new customer:

Me: “I’m sorry, ma’am, but that line is closed. I can help you here.”

Customer: “Well, you could’ve f****** told me that sooner instead of making me look like a f****** idiot!”

My head whips around at the not just the venom, but the volume of her voice. I put on my best customer service smile.

Me: “It doesn’t appear you need any help to look like an idiot.”

Yes, I got in trouble. Yes, it was worth it.