Single raised pot HU, he barrelled twice and then fired the river OOP on something like 562TK - I had 78.

This guy was drinking and just splashing on a nitty table. I can go into each decision but the important part is this - three times in the last hour he had been called on the river. All three times he insta threw his hand in the muck and took another swig of beer, he didn’t even care what people had

I thought it pretty unlikely he had anything, primarily because he was just chucking out chips without thinking. Would you ever consider ‘bluff calling’ here in the hope he just insta mucks again? It seemed crazy but I thought it was probably the best play on the river, really weird spot

No, but I would consider raising.

What types of hands has he actually shown down when called before?

If he only folds his bluffs to your raise, and insta-mucks all bluffs rather than showing down, then raising is a complete waste of money.

I did this exact thing one time, but it was a $3/$6 LHE game, not NL. I guess it makes sense, depending on the bet size and the odds he's bluffing.

Yes, but those are both big ifs.

And I said I'd consider it. A lot more info needed before I would do so.

I agree, we don't have enough information to say if calling is profitable, I just mean that the information we have been provided with so far would make raising a worse decision than without that information, not a better one.