How would you feel if you discovered that your parents are siblings?

What do you mean if .

It would explain my extreme distaste for them...

Like a niece.

"So thats why im messed up in the head"

Well I mean, my brain abnormalities would make more sense

Feel disgusted by their choice

I would be kind of horrified. And annoyed and angry at their irresponsiblity for having kids (they don't make a good combination as it is, in my opinion).
And then I guess I'd pretty much accept it. What's done is done. There's nothing to be changed about it now.

wouldn't care, it's a bit late for me to be shocked and appalled, they've done worse, and at this stage nothing done could be taken back anyhow. it'd be weird but oh well

Angry if they or their parents knew they where siblings.

Wonderful.

appalled and offended

mine aren't tho

Step I hope 🙄

Meh.

Betrayed

Aroused