My sister started dating one of those brutally honest guys a few months ago. He can be quite rude and make bad-handed comments about me and the family sometimes, which is bothersome, but my sister said he's not malicious but that he is just brutally honest and we should get used to it. I visited my parents to celebrate my sister's birthday and my husband couldn't come with me because he was busy. After the party, we all sat down for dinner and my sister's boyfriend said it was weird that my husband and I don't have kids despite being married for six years now. I was shocked that he brought this up, but I gave a short answer saying that it's because of my infertility issues. He asked on which side and I didn't want to answer, but my sister said it's on my side. I got uncomfortable as he looked at me for a second and said that maybe not having kids now is a good thing because he thought women over 30 might produce defective babies due to age. I told him it was none of his business, but he said that he was just giving his honest opinion and that's all. I, in return, told him while making candy eye contact, trust me, if I wanted an asshole's opinion, I would've farted. Literally, everyone at the table burst into laughter and my sister and her boyfriend were stunned. A few seconds later, her boyfriend excused himself out and my sister followed, then sent me a text after they left saying I was mean, disrespectful towards her boyfriend, and insulted him maliciously just because he stated his honest opinion. She also said I ruined her birthday by being petty and making her boyfriend the joke of the night in front of the family. I didn't respond, but she demanded an apology via email as soon as possible. Mom agreed that I shouldn't have said what I said and should've just ignored him knowing how he is. I think, am I the asshole? But, I'm not sure.