Jujutsu Kaisen's narrative of Ryomen Sukuna harboring a dislike for protagonist Yuji Itadori is not uncommon in the animanga. The former mocks the boy at every possible opportunity and scoffs at his abilities. Fans believe being sealed inside him is the reason for his negative attitude towards the boy.
However, Yuji turns a blind eye to it all, doing whatever he can to improve himself. He continues to develop rapidly and lives up to the potential many have seen in him. It took 248 chapters for the Demon King to finally acknowledge Yuji and pause to think about why he might have been so hateful towards him.
Jujutsu Kaisen: Sukuna's disdain towards Yuji might be quite straightforward
Ryomen Sukuna has a strong dislike for his former vessel, Yuji Itadori, due to a difference in ideals. He cannot bring himself to recognize the boy's strength. In terms of ability and raw Cursed Energy, the King of Curses is miles ahead. Thus, he finds Yuji uninteresting and weak, given he has no special prowess.
However, when it comes to ideals, Sukuna is probably the most selfish and individualistic character in Jujutsu Kaisen. Chapter 248 proves that, right from the Heinan Era, he lived for his own amusement, doing whatever, whenever, and dispatching whoever he felt like. His sole focus was on himself and on becoming the strongest.
Interestingly, that period being Jujutsu sorcery's peak likely influenced his beliefs and ideals. The time was characterized by survival of the fittest, and Sukuna viewed himself as belonging to the top of the food chain, unrivalled and above everyone else. This is possibly the reason he acknowledges people who are proficient at Jujutsu, like Gojo Satoru or even Hiromi Higuruma.
On the other side, Yuji stands as the complete opposite. He is selfless and determined to aid others, even at the cost of his own well-being. Sukuna considering himself the apex predator is balanced by Yuji seeing himself as disposable.
His grandfather's final words to surround himself with loved ones seemingly played a major role in his life. This explains the bonds he formed with the other sorcerers and the lengths he's willing to go to protect them.
His very nature is what puts him in the way of intense pain and suffering - evident when he loses people like Junpei Yoshino, Kento Nanami, Nobara Kugisaki, Gojo Satoru, and maybe even Megumi Fushiguro. These instances depict how Yuji's altruistic nature flips back on him.
Considering these points, chapter 248 explains quite well why Sukuna gets "irritated" with the teen. Yuji was unshakeable in his ideals and despite being knocked down repeatedly, he fought back. The boy backed his ideals so fiercely that he was willing to face someone like Sukuna regardless of the outcome.
Continuing, Sukuna mentions that the Jujutsu High sorcerers reminded him of someone he knew "1000 years ago". This person too probably faced Sukuna on similar grounds, backed by their ideals. A plausible theory on who this "someone" could be is Sukuna the Socerer, i.e., before he became Sukuna the Curse.
Why Sukuna and Yuji never got along
Sukuna has no respect for Yuji because he doesn't recognize his strength. Part of the reason concerns the boy's capability as a Jujutsu Sorcerer. As mentioned, the two are miles apart when raw Cursed Energy is concerned. Additionally, Yuji's Cursed Technique (whatever has been seen so far) is considered uninteresting by Sukuna. The youth relies on using Cursed Energy as a power enhancer.
However, Cursed Energy itself has been shown to have endless possibilities. When used appropriately, it can heal and regenerate limbs, defy the laws of physics, and even bend reality. In comparison, Yuji's powers are quite plain.
Another point hinges on the fact that they approached their respective levels of power through exactly opposite means. Sukuna regarded nothing but himself. He acquired what he did through his own efforts and treated others as mere tools/stepping stones, let alone comrades.
But Yuji got and is still getting stronger due to his intense desire to protect those close to him. Every bit of technique that he has learned so far has been for a purpose. For instance, he likely learned the Reverse Cursed Technique after understanding the upcoming battle's potential casualties and that Shoko could only do so much.
Final thoughts
Ryomen Sukuna and Yuji Itadori represent two opposite ends of the Jujutsu spectrum in Jujutsu Kaisen. One believes selfishness and self-preservation to be pivotal in survival and absolutely necessary in the pursuit of power, with others being mere tools to aid on the journey.
The other, meanwhile, believes selflessness and camaraderie to be crucial to reaching great heights and pursuing an ideal and sticking to it no matter what makes a person strong and gives them something to aim for. Sukuna doesn't grasp how living for someone else is a source of strength when Jujutsu Sorcery emphasizes the individual.
Related links:
Jujutsu Kaisen finally explains why Sukuna is so interested in Megumi
Jujutsu Kaisen: Does Sukuna have an advantage in Megumi’s body against Gojo? Explored
Jujutsu Kaisen theory claims Yuji and Sukuna are destined to fight each other for the right to live