is that a beer?

so at work today the manager bought us all beers cos selling coursebooks is STRESSFULL! sometimes, so we're drinking and ringing people up, and this one lady is really upset that her book is ringing up at a different price than she thought it would be. and she is giving the girl next to me shit about it, really yelling at her when there's nothing she can do about it. meanwhile i am waiting for a receipt to print and drinking my beer. and the cranky lady asks me "is that beer?" what do you think, cranky lady? no, it's a nalgene bottle designed to look like guinness.