Why does this always happen?

When you first move to a new city, you meet your neighbors, parents from sports, kids school, grocery store. Whatever random playdates and such. I have lived in the Ranch for 5 years now and looking bad at the friends I have now, I never ran into them never saw them driving. Now once I am not friends with someone I see them EVERYWHERE!
I have had some bad luck in the friend department when it comes to Ranch moms, don't know why maybe because I'm not stuck up, I don't drive an SUV (well right now) I'm not fake, I tell it how it is???  Anyway, I now run into these ex-friends all over the place. One mom I ran into at the gym, I was cordial and said hello and asked how she had been, next day saw her at the store, just said hello in passing. NOW I see a different contraversial mom driving by me almost everyday. She has dodged me in the hall at school (very 1st grade, she must have learned it from her 1st grade daughter). I know it's going to happen this summer that we end up at the same pool or something with the kids. Why does this always happen? What do you say and do to an ex-friend that you can just feel the tension a mile away?