Vass-whole

You know, I just dont get the hidden truth of the abuse asshole. I mean why 'asshole'?

Shape?
Are you trying to say ass-whole? Are you mean that u are shaped like an ass as a whole? If that, what kind of ass are we talking about here-is it like a well shaped ass or a fat one? Or is it like a regional slur,"Hey u look like a South American Ass!".
A donkey's ass?
As an abuse is one being called a donkey's hole and its thereabouts? If yes, what would a monkey's ass be? I think it'll be a compliment, especially, in the North Indian way of life where pink(or shades of red) is taken as a sign of good health. So if u see anyone in good health you'd say,"Hey u monkeyass!". But I doubt if it'll go too well with the masses as a compliment...You decide for yourself.
Output?
Is it a reference to the output that an asshole generates? So is it saying that what you give out is same in Quality as an asshole? If that be why not replace ass hole with "Bush's mouth"? I think THAT is a bigger insult...
Cheers!!