You are making some very unfounded assumptions here.

When he DM's sometimes I give him shit. When I DM (like I will be today) sometimes he gives me shit. But on the whole we play incredibly well together and it's pretty common for one of us to point out a forgotten rule, interaction or ability which would benefit the other to our own detriment.

We have been playing together basically our entire lives so we aren't afraid to get spicy every now and then like with that passive aggression.

The only time I think our play could ever become problematic is if we were both players in a long campaign together. We would probably optimize some obscene combo's that ruined the game for other players.