>I've no idea where you got this idea from. The zeroth law is not tautological, can't be derived from the other laws, and (like the third law) is often ignored in pedagogical contexts because of its relative subtletly and obscurity.

The zeroth law is absolutely tautological; it's not remotely needed because the phenomena described by the zeroth law are necessary consequences of the second law.

>Well, the entropy of what? If I put a glass of room-temperature water in the fridge, its entropy will certainly decrease.

I mean, I'm simplifying for the purposes of ELI5.

The correct description only applies to closed systems.