If tu were me, would tu post this question?

no..i'd better go and sleep..or eat a pun cake

Well, I'd post it. Because I'd be tu and not me, and tu are posting this question.

If I were you, I would not be me, and if I were me, I would not post that question. tu is the opposite of me, so tu would do the opposite of what I would do, so if I were you, I'd post that question. Not to mention that if I were you, I'd do exactly what tu would do, and tu would post that question.