Okay hear me out:
Version of the Ed, Edd n Eddy special Valentine's episode "Hanky Panky Hullabaloo" where everything's exactly the same except that first of all starts, the cupids see Double D giving the Valentine's Day card to Eddy and Sarah tries to make Eddy fall in love with him as a prank, but nothing happens. Jimmy wonders if Sarah’s arrow didn’t hit the target and she says she never misses the target. So Jimmy tries to make Double D fall in love with Eddy and nothing happens again. Jimmy fears their arrows aren’t working and complains to Sarah. She says there’s no way the arrows aren’t working and then tries to make May fall in love with Double D and this time it works, showing Jimmy that their arrows are working perfectly as they should. They spend some time thinking what happened and eventually realize what’s going on: the only situation in which their arrows would have no effect would be when trying to make people who are already in love with each other fall for each other again. They can't make people who are already in love fall in love again. And that's how Jimmy and Sarah found that Edd and Eddy have a crush on each other.
Another possible version would be the arrows to work as in "American Dragon: Jake Long". If a person is already in love with someone, the arrows will have the opposite effect and will make that person hate the person they were in love with. But I don't think it'd be so interesting to see Eddy or Double D hating each other for a long time, or maybe I just can't imagine an interesting scenario with this dynamic.
