St John's Wood is the only Tube station whose name contains none of the letters in the word mackerel.

I believe this because Wikipedia tells me so (see here). And I can't be bothered to check it, I'll just repeat it freely with an air of authority.

But what if every other wikipedia user thinks the same? So no-one ever checks. So it could be complete nonsense. Possible. But I think it's more likely that hundreds of computer geeks with lots of time on their hands have gone through the entire list of stations hoping to prove it wrong.

Although, the same geeks didn't spot that 'Charing Cross' is not an example of an alliterative station. It took a pedant like me.