MacReady is The Thing.

In John Carpenter’s The Thing MacReady gives his bottle of alcohol to a person who got his face licked by the Thing disguised as a dog.

Later on MacReady drinks from that bottle and goes and talks to Fuchs.

MacReady leaves and immediately after the power goes out and Fuchs goes to investigate only to find MacReady’s shredded clothes outside of base camp.

Later on Nauls and McReady find Fuchs charred remains and go to investigate MacReady’s room. Nauls comes back accusing MacReady of being the Thing because he finds the same shredded clothes that Fuchs found.

Meaning someone killed Fuchs, purposely removed the shredded clothing that would only implicate MacReady.

Later on, when MacReady comes back they go try a blood test but all the blood stores are ruined, so they elect to cut themselves to get new blood. However, we never see MacReady cut himself nor do we see any signs on his hands that he’s been cut.

Later later, MacReady has the idea to destroy the entire base, with all the proof of the aliens existence, in much the same way the Norwegian base was. This would literally only help The Thing as none of the potential survivors could stand the cold and The Thing could simply hibernate. Also there’s no way MacReady made it out of that explosion.

Now on to the famous whiskey scene, many people theorize that MacReady isn’t TheThing and that Childs is because Childs took a swig of what looked to be whiskey but was actually gasoline. Now this is all fine and well but I believe, based on MacReady’s proposed whiskey infection, that he laughed not because ChildsThing ingested gasoline unknowingly but because he knows that he just infected Childs via the whiskey.

I also believe that MacReady thing has no idea which form the original dog thing takes between murders and it understands that the best course of action is to be in deep cover.

There’s also proof of assimilation without outright murder via Norris.

And that’s the theory.