I developed a weird fetish because of porn. Basically I got off on guys finding my sister hot even though I don't find her attractive myself and the thought of that makes me sick. I think it was inspired by cuckold/humiliation fetishes and captioned porn pics with captions like "your sister loves your bully" I even ended up getting guys to "cumtribute" her. I think part of the reason for this is being validated by them finding something that is "mine" attractive or something.