Because they asked if she wanted butter on her bagel.
Here's the lowfat skinny:
Er, yes, perhaps. But not so strong on etiquette. She then began "yelling at the staffer to hand over her plain bagel, until the manager finally called the police."
For the record, we point out that this isn't linguistic stupidity. It is, if stupid at all, logical stupidity. Linguistically, the sentence "would you like butter or cheese" is ambiguous, in the sense that it can mean either (a) "would you like butter, or would you like cheese instead," or (b) "would you like either butter or cheese on your bagel?" Ambiguous, yes, but perfectly grammatical, and easy enough for any native speaker to understand without difficulty. In any case, such stupidity as may have been shown in the exchange really is not on the part of the barista.
Rosenthal also refuses to order using the customary Starbucks nomenclature: tall, venti, whatever. As it happens, we also refuse to do this. On our rare visits to the place, we simply ask for large or small, and have found that the underpaid young person behind the register seems to understand our quaint old-fashioned code. If he or she does feel the need to murmur venti, whether as a talisman to ward off evil or simply to be sure that the right register button is pushed, we shrug our shoulders noncommittally. We have never felt the need to hurl the F-bomb, and this despite its lamentable prominence in our vocabulary.
We do not know whether Rosenthal is truly deranged or was simply having a very bad day. But her claim to be a "stickler" makes us suspect the former. It has been our consistent observation that soi-disant "sticklers for correct English" are a pathetic bunch, who cling to their illusory and unhistorical prescriptivism as though it could save them from the dangers of an uncertain world. In this, they are like any other fundamentalists.