Funkyfunkyusopp and I came to a startling conclusion: Almost every single villian in OP has a clear psychological defect.
Let's diagnose our favourites and discuss. Just a few examples:
Buggy: Paranoid and delusional, everyone is making fun of his nose.
Alvida: Body image problems. XD
Wapol: Eating disorder XD
Arlong: Distinctly skewed moral compass. He obviously has some sort of picture of right and wrong, just one which doesn't value mankind highly.