Narcissism
Once upon a time there was a man named Narcissus. He was a greatly admired man, however, he did not admire anyone in return. Whenever anyone would profess his love for him (namely the nymph, Echo), he would cruelly reject their love. One day as Narcissus looked into a pond, he fell in love with the beautiful man in the pond -- his reflection. From his name comes the term narcissism -- excessive love or admiration of oneself.
Narcissism is a recognized personality disorder, characterized by self-centeredness. People with this disorder seek attention and praise and exaggerate their achievements, expecting others to recognize them as being superior. They tend to be picky about who they'll associate themselves with, and those who they do associate themselves with, they tend to take advantage of.
Kuja is the textbook definition of a narcissist. He thinks he is superior to everyone in every way -- looks, intellect, etc. Since he feels that he is superior, he feels that the world and everyone in it should revolve around him and his desires. Afterall, when he finds out that his life is soon to end, he proclaims, "Why should the world exist without me? That wouldn't be fair. If I die, we all die!" Kuja has no perception of other's feelings. To him, the only important thing is how he feels and that he gets everything he could possibly dream of.
Kuja does a good job of flaunting his narcissistic nature through the way he dresses. He dresses provocatively, as if to show how physically better he is than everyone else. He knows he has a good body, so he flaunts it. He knows he has a beautiful face, so he draws attention to it through makeup. Not only that, but he constantly uses terms like "ugly" and "fat" to insult people. An example of this is when he says, "Not bad... better if I didn't have to see those vermin and the ugly elephant-lady. They offend my senses." He is very preoccupied with looks, whether they be good or bad.