I mean, I don't like when the women do that. Or date siblings. But it's happened.

Dolphin, of course, with Arthur and Garth (well, Arthur and Garth were depicted as parental in early stories - I don't know if that element got dropped later (bronze age or post-COIE)).
Selina, with Slam and Sam.

Even Barbara, if you go into Batman Beyond territory.

I deeply dislike it as a story-telling device. It's just kind of "icky" to me. But I wondered if, in DC continuity, it had ever been flipped. And I mean with actual emotions involved or at least one of them being a relationship of some sort - not just one-nighters.