Originally Posted by 3Cforme

I think that's the key - deadhead vs. non-rev.

I believe (without great certainty) that DL policy prohibits alcohol for deadheading pilots and FAs. I also believe that there is no FAR (Federal Aviation regulation) around this. One certainly can non-rev out of uniform - although Delta does have a non-rev dress code. Presence of a company ID isn't indicative: one would have needed ID to non-rev.