OP:

I have no reason to doubt any of what you said here; assuming that's how it all went down you have my total sympathies. It's absolutely unacceptable and United should go above and beyond to make it right. Can only hope they do. I guess I'm left scratching my head as I've never seen anything remotely close to this. Having three drinks on a long flight is not abnormal (evening flights from east to west after a long week of work are often two scotches and a glass of wine affairs for me, with the FA's more than willing to keep the glass full.)

One thing I may add is that assuming this gets elevated, make sure you think long and hard about what - if anything - the FA may say to defend himself (is there something you guys may have said or did that was completely innocent but could have been perceived differently by the FA)? Ultimately that's still no excuse for his actions but there's a good chance that comes up. Hopefully there is someone who saw it all go down who can corroborate your story. Assuming this all checks out the FA should be looking for work.