Customers take on the persona of Louis the 14th (the Sun King) when they pull up to the drive-through intercom because they don't listen, don't take no for answer and don't use common sense. I think most customers have really terrible jobs, so whenever they have a chance to feel superior to another human they do so.
I mean, after I tell a customer that we only have two everything bagels there is really no need for him to order half a dozen everything bagels, but I had a customer do that last night. He didn't hear me wrong. He just thought I was lying to him - "You caught me sir, we actually have 20 fresh everything bagels right here at my finger tips. I don't know why I lied. I am sorry."
When I hear the beep (which means a car - or sometimes a bunch of kids on bikes - has pulled up to order) I immediately say, "Welcome to Tim Hortons, would you like to try and an Ice Cap?" and at least 50 times I have had customers say to me, in response, "No, I want large Ice Cap." It's like I am too stupid to know what they could possibly want, so even when I am right I am wrong because the customer is king and I am just the lonely jester here to screw-up your order and occasionally amuse you with my stupidity - please, please, don't cut off my head!