scapegoat

I know what you're going through.
I had a costumer at our bakery once, complaining that we didn't have some kind of bread:

Costumer: I can't find *some kind of bread, can't remember*
Me: I'm sorry, but if you couldn't find it, it's not in stock.
Costumer: It's always in stock around this time of the day!
Me: Sir, I've already told you, if you haven't found it, it's not there.
Costumer: I AM A WOMAN!!!

One of the most embarrassing moments in my life - it was my first week, too.
Luckily a coworker helped me out and even when the old woman asked for the manager, they stuck up for me.
She didn't like that, became a bit bitchy 'n stuff. Maybe that was also because the manager called her a sir first, too.