I have to chime in that it is inappropriate to drink while jumpseating in the cabin. It just opens up unknown cans of worms. It's not stuffy or self righteous, just exercising common sense.
Think about it. A conversation begins with a passenger and it is revealed that you're jumpseating while downing a Beam and Coke. Not good.
Or, how many times has a gate agent assigned you an exit row seat because you're a pilot? The FA's know that you're j/s'ing so if an emergency evac happened, it is likely that you would be called on to assist.....more so than some Joe Schmo passenger sitting in the exit row.
Look, it may not be illegal for you to drink in the cabin while jumpseating. It is also not illegal to get smashed in a bar with your uniform on (sans wings, badge or other company identifying materials). However, legal doesn't mean not stupid.
I'm a boozer myself but, I can wait until I get to where I'm going. So can you.