Funny, I had a conversation about this on fuck95 just a few hours ago.
Some guy was arguing fetishes aren't categories, and I cited incest. It's a huge fetish category with many things I like and many that I abhor.
I love sister incest, younger innocent/virgin sister preferably. Cousins are great. Don't care too much about mothers and aunts. Hate anything to do with grandmas and "GILFs".