I still had a tab open to it, so you're in luck:

My fiance [F24] and I [M21] were playing Would You Rather with some friends. We've been together for almost four years. Someone asked me, "Would you rather have one butt cheek, or have (fiance) only have one boob. We were being super casual about everything and not taking it seriously. So my non-thinking immediate response kicked in, and I said that although I really like my fiance's breasts and she really likes my butt, I'll keep the butt cheek. I don't know why I thought that would be the nice thing to do, but my exhausted and ready for bed self thought it would be. Fiance gasps. Then I thought about the answer for more than two seconds, and said, nevermind, that's silly, I'm not gonna let my fiance go on with life like that. Plus i really like her boobs, a lot. I'll lob off my butt cheek.

But even though I changed my answer, the first response was what mattered most. Stupid me. I'm kicking myself right now. She got pissed. She starts getting mad about my first answer and I keep telling her, "No, its okay. I changed my answer." Stupid me again, wrong thing to say. She only cares about the first response, saying that must be what my mind would actually rather have since it was my first response. We haven't had sex since. Not only is she now more self conscious about her body, but she no longer finds my butt attractive knowing that I apparently would rather have it than her boobs. She used to really like my butt too.

So how do I solve this problem? She's still really upset about this. I'm not even concerned about the sex life thing anymore, I just want her to know that my first answer is not the way I think, but no matter how many times I told her, "I changed my answer, I wasn't thinking at the time, I would rather not have one butt cheek," it doesn't matter. She still brings this up. A lot. And she's not even jokingly upset about it, it has actually taken a toll on our relationship.

What can I say to her or do for her that will solve this issue?