The person designated to pick up lunch by coworkers based on availability. An individual is more likely to be assigned sandwich beeyotch responsibilities if they are new to a company, straight out of college, or happen to be standing around with their hands in pockets by the time coworkers get hungry. Sandwich beeyotches are not limited to picking up sandwiches.
Hey, Phil isn't doing anything, let's make him pick up lunch. He can be our sandwich beeyotch today.