Nothing sobers you up but lots of time. A shower or coffee will just make you a more alert drunk. The worst thing that can happen is a bad hangover. If you drink enough, fast enough, you could seriously endanger your life in a few hours. Everyone reacts the same to alcohol.
Alcohol affects everyone differently based on body weight, time of day, etc.
It's none of your business if a friend is drinking too much. If you are a real friend than it is your business to talk to someone about their drinking. You can't make someone change but you could open their eyes to a real problem.