I hate this aspect of politics. No: Barnaby Joyce does not have to explain himself. He broke no laws, he did no harm. There are plenty of valid reasons to be taking issue with him. Making a fuss because he got drunk and semi-passed out in public is stupid.
Sure, laugh at him. He deserves that. He made a fool of himself. The chalk outline and the plaque are hilarious. But, he doesn't need to 'explain himself' or 'apologise to the Australian people' or whatever other stupidity someone comes up with. If he showed up to work in that state, it'd be very different, of course. But what he does in his off-time is none of my business.