Guess Who's Coming To Dinner?

I know that title is cliche' but I just couldn't resist. After all, it was my mom that used it on me last night to break some not-so-nice Christmas news. 

The family dirtbag, a.k.a. my sister's ex-husband, is coming to Christmas dinner at my parents house. I was looking forward to the family get-together but now I'm dreading it. How could this happen?

It turns out my niece and her dad (said dirtbag) were talking about him flying out here for the holiday but my mom knew he was never going to do it because he promises his kids stuff all the time and never follows through. Except this time. I think he did it to deliberately try and ruin Christmas for my parents and my sister. My dad is too nice a guy to turn this dirtbag away. He'll let him come and see the kids and even share in Christmas dinner but my mom plans on ignoring him the entire time. I despise this guy and will do my best to tolerate him but it won't be easy.

I've written about this dirtbag before but for those of you who don't know I'll keep it brief.  When he was married to my sister he was an abuser, not physically that we know of, but mentally. He gave them no money for food, he rarely came home, he treated his family like garbage.

I can't believe I'm dreading Christmas!  I wish there was some way out of this but I can't do anything without hurting my mom's feelings.  If there was a graceful way out, I'd take it.