I recently witnessed a pilot drinking a beer at a bar in an airport. He had the uniform shirt and pants but no tie, ID, wings, bars etc. However, from the shirt and pants as well as his luggage and stickers on his chart case, it was obvious he was a pilot. The appearance was that he had just gotten off of duty and going home (hopefully as a ticketed passenger and not as a jumpseater)

I'm not passing judgment as I am not sure one way or the other. This scene just made me wonder if this was proper.

That is a big no-no in my book. Unfortunately, some guys just don't get it.

Probably has a problem, but as well all know we cannot drink in uniform except at a very few company events where we are ambassadors. I am sure he thought he was "out" of uniform.

If there is a problem with this, does changing to a golf shirt or something make a difference?

File this one under "transitional moments".

Like the moment where you transition into being a full fledged alcoholic.

If you're getting to the point where you think taking off your epaulets and insignias is a cloaking device, and you are still essentially at your job site when you're having your first one, both in terms of time and distance, then you pretty much need to start work on your podium speaking skills: "Hi, I'm Bob, and I'm an alcoholic".

Most think so because that is how many commute home to have a few on the flt home.

Most FOM's clearly define "in uniform" as wearing all of the above in it's entirety. They all prohibit drinking while in uniform. Therefor one cannot be drinking in uniform if out of uniform. Perhaps wording to the effect "can easily be identified by the public as..." is in order. Poor taste and bad head work. It's not too hard to change shirts...

I like to change into my long sleeve dark blue shirt with epaulets before I down a few at the airport bar.

You shouldn't have to spell everything out in the FOM.
We're paid for our judgment and sound decision making not only in the cockpit but in public.

Maybe I'm way too conservative. But, I personally would never ever drink in the airport bar in partial uniform and/or while toting my roll-aboard and/or flight bag.

There is no "partial" uniform; you are either in it or not? I like drinking in my work shirt with no pants, but that's for another thread.