In this case, I can see why it was not identified by ground staff as he was not obviously visibly intoxicated. It was only really when he started acting irrationally - or when close enough to appreciate the smell - was it clear something was up.

From what I saw, the mood swings were real and made me think at the time just how difficult it is to manage or police this sort of thing. He looked like a normal passenger in every other way.

As noted above, it also made me appreciate how the travelling experience (and life in general) can be so different for others. It genuinely made me reflect on privilege; of course many could end up as targets for this sort of behaviour, but my guess is that his intoxication meant he could not control whatever prejudices or misogyny drove him to decide (wrongly) that he was being victimised and to lash out for it.