Seth has another great post for us:
PS When I was in business school, we did the McDonald’s case. Part of our preparation was to go to the nearby McDonald’s with a stopwatch and clipboard. We walked in the door and stood just long enough to get noticed. Boy did those guys hop to attention. Then we went to another McDonald’s and performed the following experiment (please, please do not try this at home, just take my word for it). We ordered a milkshake and a Big Mac. Ate half the Big Mac. Drank half the milkshake. We put the Big Mac remainder into the milkshake cup and went to the counter, “I’m sorry, I can’t drink this shake, there’s a Big Mac in it.” They gave us a new one.
Because McDonald’s didn’t want counter people making decisions about who to say “no” to. It was worth the expense of humoring idiots like my study group for the brand power of knowing that counter people didn’t alienate people on a sliding scale.
I think they should have called the cops on us, but you get the idea.