Ik Aoba might seem childish for holding a grudge against Kenshin, but he really is aggravating. "High and mighty" is the perfect term. He loves to look down on others and discredits Aoba's win against Hadzuru to this day, even when Hadzuru has no problem with it.
Gosh I love that this manga gives us the chance to root for someone who'd be the antagonist in any other story