The following contains spoilers for Avengers #4 written by Jason Aaron, drawn by Paco Medina & Ed McGuinness, colored by Juan Viasco and Mark Morales, and lettered by Cory Petit.
If there's one thing that can seem to be agreed on in the Marvel Universe, it's that people do not like Iron Fist.
Sure, he's got friends in various places, but Danny Rand has a knack for pissing people off, whether it's small time crime lords or immortal ninja clans. To that end, it's not all that surprising that he managed to piss off a little god by the name of Odin.
To be fair to Danny, this one actually isn't his fault. As we learn at the start of Avengers. #4, way back when Odin was the sort-of leader of the Avengers of 1,000,000 B.C., the Iron Fist of that time was a member of his group that included a Ghost Rider, the Phoenix, the first Black Panther, Agamotto (the famous sorcerer who's namesake magical artifact would eventually be in the possession of Doctor Strange), and Starbrand. Despite their various differences, they did manage to defeat a Dark Celestial and apparently conversed rather frequently, so they were nothing if not efficient and well aware of each tother's powers and personalities.
Though his opinions on his former teammates vary -- the Panther of that time impressed him, but Agamotto infuriated the former Allfather -- he didn't have the highest opinion of the Iron Fist of that era. In fact, he doesn't have positive thoughts for any Iron Fist, across the various users of the mantle. Whether he's actually met all of them over his long period of life is ultimately irrelevant, since none of the one he is familiar with did much to change his opinion of the overall "brand," as it were. (Even Pei, the other Iron Fist of the present day, apparently can't change his mind, and she's pretty awesome.) His hatred is so strong, Odin straight up tells Thor and Hulk to never trust anyone that hails from K'un L'un, the bitter old man further grousing about how he should've "burned that wretched dragon's nest" down when the opportunity arose.
It's unclear what it is that made the Allfather have such hostile feelings towards the Immortal Iron Fists, but it wouldn't be surprising if this minor detail were revised later in Aaron's run if Danny ever ends up an Avenger again. With a rotating slot on the team that will soon see Doctor Strange's spot be taken by Domino, Rand certainly has the opportunity to join this iteration of the Earth's Mightiest Heroes. Were he to be included, we may get more insight into what issues the Iron Fist and Asgardian of prehistoric times had... or we may get a fight between Thor and Iron Fist. Since the present day Ghost Rider and Starbrand got into a fight in Marvel Legacy that was part of a rivalry dating back to the Stone Age, there may be a similar altercation in store for Danny and Thor down the line.
On some level, it's not all that surprising that Odin continues to hold a millennia long grudge against Iron Fist. Given how rude he was towards Jane Foster when she was operating as Thor, it's obvious the Allfather isn't exactly the cool, calm and collected type. Aaron's run on Thor began with the sins of Thor's past come back to haunt him, so it's only fair that Aaron kick off a genuine Avengers run with Odin's sins coming back to haunt him. The good thing about this is that if Iron Fist does meet Thor, the two may break the cycle and come together to help save the world.