If I see an ex in public, I'm instantly filled with dread. Best case scenario it's someone I don't want to talk to anymore and that tension will make any encounter uncomfortable. Worst case scenario they might go monkey if they see me with someone new or know a bunch of personal shit I don't want them gossiping with others about. Even if they're totally normal and fine with it, their new partner might not be and I face the same threats from them instead.
I would hate to be in the same org as an ex. There would never be a normal working dynamic between us and there would always be at least one person with motive and means to backstab me. If I don't go to the same roller rink or climbing gym as exes, there's no way in hell I'd do something politically radical around them.