rancideous

To describe someone or something as rancideous is to say that they are the absolute epitome of being ugly or unpleasant.

That person over there is so completeley rancideous that if I have to continue looking at him, my eyes are going to explode and my head will catch fire.

This meal is rancideous. I hate it. You have insulted me by asking me to eat it. I wish you would die.