Well, I was going to say hemlock tea and drain cleaner but that doesn't match up with everyone else's answers.I will go with alcohol and caffeine drinks.
alcohol and anything sugar based....the body has to work harder to burn the sugar, and makes you hotter....water, or vitamin water is the only and best way to go to rehydrate and feel cooler and not thirsty...
milk
*gag*
Hot chocolate
Due to the dehydration.
Cheap orange squash full of E numbers :-(