From Animal Man issue 2:
You don't see that happen very often.
I miss Aquaman-as-king. I know we've got him back in Brightest Day (which I am very pleased about) but I miss his role as King and leader. As King, he's got a very special niche among superheroes. The other members of the JLA choose to be responsible for civilians. They operate outside of the law and they can choose what rules to follow. Aquaman is different - as leader of a nation he is responsible for his subjects regardless of how he feels about them. He is bound by law and convention and he is accountable to them. He cannot just do as he pleases, he has to sit in on councils, pass judgements, carry out redevelopments of broken bits of Atlantis and be the mediator between the surface world had his world.
He must feel pretty disdainful of the rest of the JLA - they choose to put on the tights and fight the good fight, but they don't have the same kind of responsibilities as him. I guess Diana as a princess comes closest, but even so, she has a very different role to Arthur. For a start, Princess and King sit differently on the scale of royal hierarchy. Diana chose to leave Themyscira and go to mans world - Arthur cannot just up and leave his subjects. I know he's been booted out a few times, but that's different to voluntarily leaving. Back on Paradise Island Diana is not responsible for matters of state. although of course she takes an interest. Arthur's role is all matters of state.
Then I think that the culture of Atlantis and the Amazons is very different, which means that Arthur and Hippolyta reign differently. Each country has different requirements and protocols and a different relationship with the rest of the world.
No wonder Arthur gets so pissed off with surface dwellers. Surface dwellers poison the seas on a daily basis. At least the Amazons don;t have to deal with that quite so regularly.