What do you think about me ruining a party over a sexist remark?
Why do you think you need to ruin it?
He always makes sexist remarks when in front of women in my opinion.
While I think I would also call out a person if they are being sexist, I don't think ruining their party is the best way to do so, in my opinion. I would first talk with them privately, so that they would not get humiliated, as you are not sure if they know that what they are doing is wrong.
I believe that I am going to ruin the party.
While it is good to call out sexism, you should respect your host and not cause a scene at the party. I would just pull them aside and mention it to them instead of trying to ruin the party.