I believe I was rejected after a job interview because of not drinking.

Another boss I had any a different job told me he fired someone for not partying with everyone else. If you went to these parties and didn't drink, the boss would harass you all night.

I agree with you that many people are just self conscious, but it's not exclusively that way.

Both of your cases sound like shitty places to work.

I was once rejected from a job interview at a DC startup because I didn't order a beer when they took me to lunch.

This seems a reason so stupid to reject somebody that either a) they didn't like you but didn't want to tell you the real reason, but didn't care enough to think about a plausibly sounding fake one; or b) you dodged a major bullet as these people had seriously messed up priorities. I'd bet on a) but can't exclude b) completely of course.

Even if that is what they said, do you honestly believe that was the real reason?

Beyond the slightest doubt.

Well, it's safe to say you dodged a bullet then :)

Interesting. What do you mean by self-conscious ?

https://psychcentral.com/blog/archives/2014/01/26/how-to-be-... for examples.

The tl;dr is that people who are insecure will attempt to rationalize their feelings, and this frequently includes feelings of judgement and persecution from others where none exists.