I'll just chime in with a me too here as well.
It isn't so much a matter of law, but one of company SOP or policy or whatever, and furthermore one of professional conduct. Before duty, after duty, on halloween, or in your backyard in front of the BBQ after work, it's not a good idea to drink in uniform.
Do I have pictures of myself shotgunning beer in uniform, hell yeah who doesn't? Just not on the crew bus eh.