It's not rude because the woman has taken nothing from the clerk. By stating it flatly, as you describe, there is no undermining of the clerk's position. Even I

It's not rude because the woman has taken nothing from the clerk. By stating it flatly, as you describe, there is no undermining of the clerk's position. Even IF the subtext is "you're pissing me off", she's still given both of them the benefit of ignorance so they can continue the facade. It's the clerk who chooses to be offended outwardly by it, rending herself even of her own dignity, for, what, maybe to try to make the shopper feel bad for saying something that _could be construed_ as subtextually rude? All she managed to do was give her power away for passive aggressiveness.