I have some of my best workouts if I know I'm going out drinking that night. You know good times are coming so you have fun even in the gym which usually means a better workout. Life's to short to worry about every single workout. Birthdays are only once a year, workouts are 4-5 a week, you'll be okay. So go lift, get drunk tonight and pick up some skanks at the local bar and eat shitty all day tommorrow while watching the playoffs. Thats an awesome plan!