I'm generally sober when my friends are drinking because I can't drive and well I don't want to end up drunk and stuck somewhere.
Because I can't drive, I'm never the DD, but occassionally I do get frustarted with my friends when they are all drunk.
Several times I've had friends who would go out with me and want to drink and then get mad at me because I didn't want to. I had one friend say to me once, 'I don't like drinking alone' and then somehow I ended up drinking with her, and eventually had to pull her off some guy she met at the club because she wanted to go home with him. Things like that don't make me like hanging with my friends when they are drunk.