Living in DC
Whole Foods, P Street, yesterday. My groceries are all bagged, I've swiped my debit card through the debit card reader, and I opened my wallet to extract a twenty-dollar bill.
"Oh, and can you give me a ten and two fives for this?" I ask the young lady at the cash register.
She gives me a look like I've either asked her to discuss string theory or murder the person behind me.
"How are you going to pay for the groceries?" she asks.
"On my debit card," I say. "I just passed it through the reader."
"Oh," she says. She punches a couple of buttons on the register, takes my twenty, gives me the change, and hands me my receipt.

I guess I didn't realize I was being so... obtuse.