The most frustrating thing about Kim is how she's immune to criticism. Her apologies are almost always met with the other person apologizing, even when they shouldn't have to.
"But Kim apologizes and learns her lesson! She grows and matures past those things! It's not fair to hold it against her forever!"
"Bueno Nacho" - Apologizes for getting mad at Ron for outshining her at the job. Not for forging an application for him or guilting him into taking the job in the first place.
Bonus: This is the first of Kim's apologies, and she consistently apologizes for the most minor transgression of the episode, ignoring all the other ones.
"Attack of the Killer Bebes" - Says she'll support Ron because he's her best friend, but doesn't actually apologize.
"The New Ron" - Apologizes for saying Ron needs a new haircut. Not for forcing him into one. Not for not caring how much he hated it. Not for stealing his hat. Not for humiliating him. Tries to throw in a lesson at the end that it's what's on the inside that counts, ignoring that fact that she was the one who forced him to change in the first place.
Bonus: Once again, Kim only apologizes for the most minor transgression.
Bonus+: There's a scene where Kim gets mad at Ron for "abandoning" Rufus, but, having watched the episode recently, I can say that's not what happened; Ron, despite not having pockets, still carried Rufus around with him, Rufus wandered off on his own. Ron probably wasn't too worried because Rufus does that frequently. And he does gently chastise Rufus for wandering off anyways. Thus, Kim's anger at Ron was not justified, and likely just because she was looking for an excuse.
"Coach Possible" - Never actually apologizes for driving her brothers' soccer team so hard they cry. Doesn't apologize, but does get fired from a job she didn't want in the first place, and mopes about it.
"October 31st" - Doesn't apologize for the lying or putting other people in danger. Doesn't acknowledge that she was putting other people in danger.
Bonus: How would Monique's family react to finding out one of Monique's party guests destroyed their garage door? Probably not happy, and banning Kim from their property until she can pay off the replacement wouldn't seem unreasonable.
Bonus+: I doubt the people asking Kim to retrieve the Centurion Project would've been happy to find out how it got stuck to her in the first place. I imagine Kim would be getting much fewer retrieval jobs after that.
"The Twin Factor" - Doesn't apologize for using mind control on her brothers. Tries to justify it and, though her parents clearly disapprove, isn't punished for it.
"The Ron Factor" - This would have been a great episode about Kim learning she takes Ron for granted and apologizing, but instead, despite doing practically nothing in this episode, she still has credit handed to her.
Bonus: The Global Justice scientists said the results of their study into "The Ron Factor" were complete and that Ron was a non-factor, but there's a movie about how Ron is vital to Kim's success, so clearly this is false. Perhaps they meant they couldn't replicate it?
"Adventures in Rufus-Sitting" - Lies to Ron about how it went watching Rufus. Doesn't apologize for not taking it seriously. Doesn't apologize for accidentally endangering Rufus. Just lies to him about how it went.
Bonus: My sister has mentioned to me that how someone treats a pet says a lot about how they view the pet's owner. So Kim's treatment of Rufus says a lot about her opinion of Ron.
"Return to Wannaweep" - Doesn't apologize for not taking Ron's concerns seriously or sabotaging Bonnie. Even Dr. Lurkin apologizes for not taking Ron's concerns seriously. And then Ron tries to give a lesson about how if Bonnie and Kim weren't so busy competing with each other, one of them could have won the Spirit Stick, as though Kim and Bonnie are equally to blame for it.
Bonus: Someone who hasn't known Ron as long as Kim has, has enough respect for Ron to apologize to him, when Kim consistently fails to do so.
"Bonding" - Apologizes to Bonnie for an unintentional comment about Bonnie's weight, quicker than she's ever apologized to Ron, and more sincerely as well.
Bonus: Despite not actually intending to insult Bonnie, Kim still has enough respect for her to apologize. More than she usually does for Ron, her "best friend".
"Fashion Victim" - Apologizes to Monique for being jealous, but not the things she did that could have cost Monique her future in the fashion industry.
Bonus: If Monique was hassling Kim to break an NDA and trying to get a tech guy to find a loophole so she could, would we think Monique should be forgiven so easily?
And consistently doesn't apologize to Ron for dismissing his fears, concerns, and feelings.
So, Kim apologizing to Ron is very rare, almost non-existent.
It's been mentioned to me that some relationships don't require explicit apologies or that love means never having to say you're sorry.
If you care about someone, and you hurt them, you should want to apologize and make things right. Even if it seems like you don't need to say it, you should still show you're remorseful in some way.