You had one too many last night. You're exhausted and hungover and just can't get out of bed this morning. But it's time to get going, you have to be somewhere. One of your friends starts making a pot of strong coffee while the other turns on the shower, cranking the dial to cold. Without further ado you're shoved into the shower for a few minutes, then handed a cup of hot coffee. This will surely chase away your hangover and get you up and at 'em.
It's true a cold shower and hot, caffeinated coffee might perk you up a bit. But neither one will cure that hangover. That will only happen once all of the alcohol is out of your system and your body resets itself. Drinking coffee, by the way, could actually make your hangover worse. Alcohol dehydrates you, and coffee exacerbates dehydration since it's a diuretic. So swap out the coffee for water, especially if you've been vomiting, which is yet another cause of dehydration [sources: Peterson, WebMD].