wo characters have a massive rivalry, their kids meet up at one of their showdowns and while the adults are busy hating each other, the kids just sort of stand off to the side and be like,
A. "Are we supposed to hate each other?"
B. "I think so, but that sounds like a lot of work, so lets not."
A. "Sounds good to me."
Then they show up to their parents fights and cheer them on like (american) soccer moms. One of them brings drinks and the other brings snacks, and they sit on the sidelines cheering while their parents are busy obliviously hating each other.
The kids become good friends and start hanging out and eventually dating, and by the time their parents find out about it they've already been going steady for a year.