The Contractual Obligation Implementation - S6-E18
Factual error: At the end of the episode, the girls are at Disneyland in costume as Disney Princesses. Adults at Disneyland are not permitted to wear character costumes because of the risk of them masquerading as Cast Members, so they certainly would not have been dressed that way at Bibbidy Bobbidy Boutique.
Chosen answer: It does. The variable cleanliness of the cab and the habit of taxi drivers to engage customers in small talk would be too much for Sheldon to handle, and not an option for him.
Captain Defenestrator