tact is not my strongest suit
There really must be a polite way to say "thanks for going to such a great effort to inform me about something I already knew", right?
(In English, by the way. There's no point in even remotely trying to convey it in Japanese.)
(In English, by the way. There's no point in even remotely trying to convey it in Japanese.)

no subject
But I usually don't worry about that, if I'm being treated like a clueless schmuck.
せっかく教えてくれましたが、、、知ってましたよ、最初から。