The Euclid Alternative - S2-E5
Question: Though it comes up in other episodes as well, this one is focused on Sheldon needing a ride everywhere he goes because he can't drive, not to mention his not being welcome on the bus. Of course, this story element would be nonexistent if there was a simple answer, but it does beg the question: Does Pasadena not have taxicabs?
Answer: Sheldon DID finally use a taxi when going to the airport to see and propose to Amy in New Jersey.
The Decoupling Fluctuation - S6-E2
Question: Why does Bernadette seem surprised to hear that Amy can see her and Sheldon eventually getting married?
Answer: Bernadette is surprised at the thought that Sheldon could get married. Going against everything she knows.
The Sibling Realignment - S11-E23
Question: Why did Mary say that she'll only be at Sheldon's wedding if he invites his older brother Georgie, if she's on bad terms with him? Is this because she loves him deep down even if she calls him an idiot?
Answer: Weddings are a family affair and Mary doesn't want Sheldon's stubbornness about his brother to interfere with family.
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