I don't so much mind Karna being rude to those who were his antagonists. Like if a serial was true to the story and depicted him as being rude towards Bheeshma or Drona, it'd be one thing. Or for that matter his hostility towards the Pandavas.
What bugs me is that Karna is getting to be depicted as guilty of ingratitude, which is the farthest that could be from reality. In the original, the reason he stayed loyal to Dury to the end was his gratitude to the latter for standing up for him, and then taking him into his close circle. The reason he was rude to the Pandavas, and hated them (until he found out who he really was) was that they spared no opportunity to insult or hurt him.
But here, in this story, Pandu, Kunti and now the Pandavas are very polite towards him. They've bowed to him, despite being of a superior (known) status. Had Karna been true to character, he'd have loved and supported them. Also, Karna always graciously accepted any hand of friendship that came his way. Yet, in this serial, when Kunti extended her hand wanting to feed him, he was extremely rude in his refusal to let her. 😡
If the makers didn't want to follow Vyasa b'cos it doesn't paint Karna in the best of lights, then they should have changed it to something that was at least logical. Like having invented Karna's encounters w/ Pandu and now the Pandavas, they'd have been just fine in making Karna allied to the Pandavas, up to the war, and fighting it on their side. That would have been consistent w/ a combination of Karna's character and the one they've created in this show - the kid who's showered by love from Kunti and her family.
The main reason Karna fans hate Kunti was not merely her floating him away in the river, but rather, never acknowledging his identity or doing anything for him until she needed him. But in this story, Kunti does not do that. Even though she doesn't yet know that Karna is her son, she gives him almost the same love that a mother does, and in fact, in his childhood, loved him more than Radha did. So given this combination of circumstances, they should just make Karna all out pro Pandava and have him fight on the Pandava side in the war. Granted, it will be completely nonsense, but it will at least preserve the integrity of Karna's character.