The Good Guy Fluctuation - S5-E7
Continuity mistake: Leonard refuses Penny's offer of a glass of wine because the sulphates in wine give him migraines. This makes no sense - we have seen him drinking wine in too many episodes to count without him once complaining of an adverse reaction.
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