They were both human at the end, deal with it

Why should we assume the thing has combined all its mass into one being, it could have kept somebody separate who Childs was chasing

Childs' breath is visible, John Carpenter has gone on record saying hes not a thing, and every sequel comic or video game ever made has him not be a thing (at that point in time)

niggers can't be relied on to do any job

Alcohol like whiskey burns too

I know I'm human. And if you were all Taylor Swift, then you'd just attack me right now, so some of you are still human. Taylor Swift doesn't want to show herself, She wants to hide inside an imitation. She'll fight if she has to, but she's vulnerable out in the open. If she takes us over, then she has no more enemies, nobody left to kill her. And then she's won.

Coffee doesn't have alcohol in it...

Yeah. They both were human and that's the point of the ending.
Shits so bad that they couldn't ever readily trust the other to NOT be The Thing by that point. Either one of them could be The Thing at any moment. They would be doubting themselves too.
I believe Pliskin knows this and intentionally attempts to poison both of them so The Thing can't escape with a host.
Of course the videogame kind of retroactively changes this a bit.

The entire movie is just a hallucination induced by cabin fever, hypothermia, and Palmer's weed. There were never any aliens or imitations, just a bunch of guys going crazy in the snow and killing each other like the Dyatlov Incident.

Another debatable theory that arises from whether or not Childs was an imitation is the scene where Palmer hands Childs his cigarette while they're watching a quiz show on a monitor. As it was around the time MacReady and Copper returned to the base, Palmer may have been assimilated at this point, and possibly once he passed the cigarette to Childs, it may have been contaminated at the time, leading to further speculation that Childs may have been an imitation as well.

Kurt Russell came up with the final moment with MacReady and Childs during filming. Likewise, Russell came up with the final line of dialogue, and what a phenomenal line it is. On that note, it should be mentioned the only screenplay Russell has ever received credit for was Escape from New York (1981). Although the screenplay for that was drastically different than the finished product, we have to say you can't win 'em all, Kurt. Carpenter still doesn't know whether one, both, or neither of the men at the end are the Thing.

The reason Child's abandoned his post as he claims later to have seen Blair outside. It seemed like a rational statement, as he knew for sure there were only three other people still alive and one person who they were not certain about. Since the other three survivors had left in a group, the one isolated individual walking away might have been the Blair-Thing, having escaped from the shack. Also, moments after the group see Childs run out of the base, the power goes out, suggesting Childs did see Blair. Of course, all of the survivors were both under a lot of stress as well as exhausted and sleep-deprived, which would have made it harder for them to think clearly, so it possible that Childs was hallucinating or that his mind was otherwise playing tricks on him. It's interesting to note; when the group goes to give Blair the test, there is a long ominous shot of the facility. The camera pans into the coat room where Childs was guarding, Childs is gone, the door has been left open and snow had begun to build up at the entrance. Moments later, Nauls sees Childs run outside. It's possible Childs was attacked and assimilated, and we see the now-infected Childs run off into the storm. It's also possible that Childs was searching all around the facility for Blair and we simply see him running through a corridor.

that's stupid head cannon shit. the movie ends the way it does for a reason

We know 1 has to be the thing because of carpenter but the rest is ambiguous. Why would childs take that sip anyways? If he was human he risks contamination right there on the spot. I start to wonder if carpenter was full of shit when he said that and the truth is that they're both the thing, they will make it off the island, all of humanity is fucked.