I was in (insert name of expensive clothing store) when I asked one of the truly stupid and "hello, I'm the mystery shopper!" questions that some MSCs require (you know, a question no one would ever really ask, that immediately gives you away?). The associate answered then suddenly looked panicked and asked
"you aren't a mystery shopper, are you?"
Per my training, I looked confused and said "what's a mystery shopper?"
He heaved a sigh of relief and said, "oh, thank God, 'cause when the mystery shopper's here, it's HORRIBLE! Everything has to be clean and folded and perfect, and she only comes in for like 5 minutes, so bad!"
I didn't report him when I filled out the shop report, but realized later, that if I owned that store, and the associate went off on a customer like that, I would TOTALLY have fired him. If it ever happens again, I'm reporting it!