Lightning McQueen wrote: They are "ex" for a reason, just smile and wave, it really annoys them when they can't annoy you.
True enough.
My first wife and I parted company in mid-1975 after 7 years of marriage, but kept running into each other in places where we had common interests.
First she was a bit snarky when I rolled up in my new 260Z, then when she saw me with the Israeli Army Sergeant (female) I was dating while she was in Oz for 3 months, and a few years later when I turned up in the dog pavilion at the Royal Show with the younger half-French girl who became my second wife. All that despite the fact the ex had moved in with a guy she eventually married only 3 months after we parted.
It even showed to her family - on one later occasion also at the Royal Show her sister said
"Don't be snarky with my favorite ex brother in law!" and came over and kissed me.
The second wife lasted until she died in 2008 after 24 years together.
I met number 3 in 2014 and we married in November last year.