Yes, caffiene will make you have to pee more often.  But the suboptimal drink that you’ll drink is better than the perfect drink that you won’t.

If you need to be hydrated–and you do–and the only thing you can tolerate cold is Coke or iced tea or whatever?  Drink that, only more of it.  Alcohol is still bad, because it uses up water in its processing, but caffiene?  Eh.

I’m thinking of Pennsic here, of course, but it applies to anyone living in a hot climate.