TFL also hits my own personal pet peeve of web design. The online form for registering an oyster card has a phone number field. Which is perfectly standard. And it has a check to make sure you input a valid phone number rather than "fuck off, you don't get to telemarket at me". Which is also standard enough. The problem is that it insists that my perfectly valid and functional 10 digit phone number can't possibly exist. If you're checking whether something is a valid $whatever, then for the love of all that is good and holy, please check the specifications for that whatever first, so you odn't piss people off. (This problem is far more common than it ought to be. TFL is merely one such offender. But like I said, it's my pet peeve.)