how do you deal with meeting an ex? Adults only respond please.?

[conusgypsy]

I've never met an ex before, but the one experience of an ex I had over the phone was very negative. I have no respect for my s/o's ex. In my opinion she is extremely unethical, immoral and takes no responsibility for her actions - a total deadbeat. Because she lives so far away, I've never had to meet her; however, my step son will be graduating in May and she will more than likely come to town for the graduation (if she can bum the money from someone to travel). She was verbally abusive to my s/o when they were together and neither one of us wants anything to do with her. What is the best way to deal with this? Should we completely avoid her and ignore her if we do cross paths or should be give a luke warm hello or be friendly and do the formal introduction? There will more than likely be future (although very few) family events together and I'll have to deal with her to some degree in the future, but she is not the kind of person I would like or talk to even if she weren't my s/o's ex. Very anxious about the potential meeting...suggestions please.