A little over a year ago, one of FI's groomsmen became involved with a married woman, Tiffany.
He considers her his "girlfriend" (His status on FB is 'in a relationship') even though she is still married, and bounces back and forth between living with her husband, her parents, and occasionally Karl, when her husband and parents get tired of dealing with her.
Basically, the woman is a wh0re. While "dating" Karl, (in addition to being married) she started sleeping with his best friend, Ryan.
Any time they are together, Ryan is with them, and the two of them are all over each other. Karl knows they slept together, and broke it off for a while...but is now seeing her, again.
It makes our entire circle of friends disgusted to see it. The last time they came to FI's and my house, I was on the verge of asking Tiffany to leave, because it was so blatantly obvious what was going on, and Karl was just...sitting there, all stoney faced and miserable. On the rare occasions where Ryan isn't around, she finds another male to latch onto, still in front of Karl.
Now, I get that this is HIS problem to deal with, that if he wants to put up with her cheating on him (can it be considered cheating if she's married to someone else already???) and rubbing it in his face, its entirely his decision...But I don't want the woman at my wedding.
So, my question is, even though he considers her to be his "girlfriend", do you think I can get away with not inviting her? I'm...ok with being rude, to avoid seeing Tiffany dry humping some random man on the dance floor, while Karl drowns his sorrows with umpteen glasses of wine.
Also, I prefer the more polite route of inviting Karl, and on the RSVP card, indicating that we have reserved 1 seat, etc. I may be wrong but I feel like he's intelligent enough to know what that means.
But FI thinks that he needs to tell Karl, explicitly, that she is not welcome at our wedding, and that if she shows up, she'll be asked to leave. He's afriad that Karl will just assume that he can bring a guest.
So, in this situation, I'd like to know what you think A) proper ettiquette suggests, and also
What YOU would do, etiquette rules be damned.