I'm bad. I'm the type that would walk in there and say, "I was told my bike would be ready in two weeks. It's been four. I'm here to pick it up, how much do I owe you?".
Then stand there with this look on your face of utter excitement. Then as they tell you your bike has not been started, say with that same excited (but cordial) look, "Oh okay, then I'll wait. What, a couple of hours good?" And then start to browse the store.
When they tell you it's not going to be done that day, I'd say (with a bummed out look), "Wow. I've waited all this time and now I'm a little disappointed. I brought it here because of your fantastic service and the expertise. I guess you don't have time for my bike. I really need my bike by tomorrow for I had counted it on being ready. But I don't want to add to your work load. Is that my bike over there? Let me get it out of your way."
Then as you roll away, thank them and tell them you were sorry to bother them.