Get in the shower and remove the shower head. Run cold water over your femoral arteries (upper inside of your thighs) for 10-15 minutes until you are on the verge of shivering.<p>This is highly effective as the femoral artery is a major blood vessel and running icy cold water over an extremity is a lot less unpleasant than running it over your core.<p>edit: I refer specifically to the UK as it is <i>particularly</i> hot here at the moment, but obviously this applies anywhere where most people don't have AC