I normally take 1 day off, maybe 2 if I am feeling really shitty. Then I get back in the gym and take it easy. You don't want to be busting out 90% + lifts or anything, but moving around and doing some lighter stuff can get you moving and help to flush all the yuckies out.
After drinking.... well you are in trouble there because you most likely will barf or poo your pants during a metcon or a heavy squat workout if you are hung over. Also, getting drunk is rumored to take off a week to two weeks of your training, so going in and lifting heavy will most likely not be a success.