I know this has been written about many a-time, but I can't resist.
It drives me freaking cuckoo bananas when I have this conversation:
Customer: "What soups do you have today?"
Blondie: "Our soups of the day are chicken noodle and cream of broccoli, but for an extra charge you can have fried onion or chili."
Customer: "Do you have split pea?"
This can be applied to many different scenarios, which all drive me equally batty. Vegetables, breads, etc. Looking dejected and asking for something I didn't list is not going to change my answer. It's not like when you visit your hookers downtown and you have to tell the truth if they ask you if you're a cop (is that even true?).
I would not lie to you, at least not right off the bat. Now that you have asked me a stupid question, I hate you and will subtly exact my revenge.