"Tale Of The Sandwich Trailer" joke

Here's the background:
Bill works in a coffee, bagels, and sandwiches trailer on the campus of CSUC; Chuck is his boss and the owner of the truck, and yes, according to Bill, this actually happened. (Chuck is telling the story).
Her: Yes, I'd like a milk with some coffee in it.
Me: So, that's just a splash of coffee in a milk?
Her: No, a regular amount of milk, but not coffee.
Me: Is there more milk or coffee?
Her: Oh, definitely more coffee.
Me: So that's a coffee with some extra milk.
Her: Just the usual amount of milk.
Me: A coffee with milk.
Her: Yes.
Me: Anything else?
Her: A little extra milk and do you have coffee with no caffeine?
Me: We do have decaf.
Her: No, I don't want decaf, just some coffee without the caffeine.
Me: Ma'am, that's what decaf means, no caffeine.
Her: Oh, then do you have milk with no caffeine?
Me: Milk doesn't come with caffeine.
Her: Yes, it does.
Me: Not that I know of. Where do you get your milk?
Her: It doesn't say caffeine free on the milk so it must have caffeine.
Me: Oh, you're right, my mistake, I forgot that we get the decaf milk. No problem - we have only decaf milk. Anything else?
Her: Do you have any bagels?
Bill: (who has been listening all along): I'm sorry, ma'am, we're all out of decaf bagels.
Her: Well, what are those? (pointing at sesame bagels)
Bill: Those are sesame donuts with extra caffeine added.
Her: I guess I'll just have the coffee. Do you take credit cards?
Me: No ma'am, cash only.
Her: What about Visa?
Me: Is that a credit card?
Her: Well, yes.
Bill: Is it cash?
Her: No.
Bill: Then no, we can't take it.
Her: What about checks?
Me: Cash, ma'am, nothing else.
Her: O.K. How much is that?
Bill: Eleven dollars and 45 cents.
Her: Really?
Bill: New war in Alaska is ruining the coffee business, plus you wanted the coffee with no caffeine, that's hard to find now, had to grow it myself.
Her: O.K. (proceeds to write a check)
Bill: Please leave.
Her: Why?
Bill: You're raising my blood pressure, leave now.
Her: But what about my coffee?
Bill: Leave and never return.
She leaves, but pays the $11.45 first. In cash. Seriously.