I am also terrible at punctuation and have a terrible time remembering which side to put the "$" when referring to money. As far as capitalizing pronouns, it is a bad habit that I have and something I unconsciously do. It has never been pointed out before and I'm not sure if I should thank "you" or not as your comment comes off a bit like an ad hominem attack. I am actively making an effort to be more positive so I will assume your intentions were good and instead say.
Thank you or Thank You? How about just Thanks for pointing it out!
To me, the capital You reads kind of aggressively. It adds an unusual amount of emphasis to the word which only/mainly happens when an upset person is making an accusation.
I don't think they meant anything mean or critical by it. Just curious like myself. Thanks for answering btw.