Inappropriate conversations

Okay, maybe I am WAY off base here but this is something that has been bothering me and so I would like some opinions.

First, have you ever NOT liked someone's sibling? You know, you have a friend or an acquaintance and you do not like their family? Do you actually TELL them that? I know I never would. Why? Because it's inappropriate!

So here's my situation: My sister is dating a man who my husband and I used to be really good friends with - actually we were really good friends with him and his second wife. We liked him, the wife? Not so much. We always hung out together, I thought we all got along fine - she is super intelligent and a bit socially awkward - but I always welcomed her in my home and was nice. We found out withing 2 weeks of each other that we were pregnant, we got married a week apart and our kids were born the same day! Wild, right?

Later on I came to find out that she told all of my friends at my wedding that she did not think that Frank should marry me. Who does that?? She didn't even KNOW any of my friends but felt the need to share that opinion on my wedding day. Freak.

Okay back to present day...so they are separated and my sister is dating this man and it seems that whenever they have to see his wife (no one knows when that divorce will actually happen) she finds the need to bash me to my sister. I find this very odd. My sister finds it funny because she knows that I don't like this woman. But it is weird to me that these two woman find the need to even discuss me. I realize that I am the only common ground that they have (well, except for the guy) but really? She told my sister that I used to come around "shaking my ass and dancing around" in front of her husband. You want to know what's funny about that? My husband was always there and he never saw such a sight.

So now, I have not seen or talked to this woman is almost 13 years and she is STILL carrying on over ...whatever? But here's the main thing, I guess, that is bothering me - is this woman bringing me up on her own because she is just a miserable, bitter freak or is my sister egging this on?

Either way, it is bad manners on both of them. I have had many friends over the years whose family members I could have done without but I kept that to myself! So what do you think? Do I let this high school behavior nonsense bother me or do I just laugh it off?