For those who work with the public: What was the worst situation that occurred between you and a customer?

I misgendered a woman who was already very irate. This was probably 30 years ago, before trangenderism was as common as it is now (or at least as publicly presented). It did NOT go over well, to say the least. Other customers were smirking and giggling, and even a coworker was having trouble keeping a straight face. In my defense, she was heavyset, had shaved hair and a raspy voice. Luckily I didn't say any of this to her. I just got my manager and let her yell at me (and him) for 10 minutes. I learned the value of keeping your mouth shut until you're certain that day.