Hmm - interesting...
I have the gross misfortune of actually working alongside my ex-girlfriend - she's a particularly nasty piece of work! Ha! Ha!
She moved out a year ago, saying she wanted her "independence". I was really supportive. I thought work was getting on top of her, and she needed a bit of space - no IDEA that meant shacking up with one of my (former) close friends, whom I ALSO work with! Oh, well - Better that I found out then than later on, I guess. It's not that it didn't hurt - it really did. Hell, I'd bought the ring and everything - AND I signed as guarantor to her flat just up the road from me. What was worst of all was that she'd not even said goodbye to my little 6 year old, who'd absolutely loved her - and that was horrific for a solo dad to deal with for a time.
It was easy to sort things out in my case. I put EVERYTHING she'd given me into a collection of rubbish sacks (shirts, watches, books, music, DVD's, video iPod, etc...), and put aside all the things that she'd forgotten to take with her (including her nice, brand new golf clubs, with which I did a bit of gardening in my flower beds with first), went back to work and dropped everything at the guy's feet - in front of everyone - telling him to stick it as far as it would go. Sideways.
Made ME feel a helluva lot better, I can tell you!
The sad thing is that she's just done the same thing to him now... Nothing like pathetically habitual behaviour. I'm talking to him again, but can't STAND the sight of her. My little boy, by the way, is as happy as he was before, and we're enjoying a very happy life together on our own.
So, in answer to your question, ignore 'em. Don't even lose sleep over them again! I don't even acknowledge her presence (although not in a malicious way) and it makes MY day seem so much better - for I know I'm a better person from it.