I like things that aren't classically romantic.

There's one set of characters who hate each other and bond over beating the shit out of each other (it's mutually consensual. If furniture isn't breaking, they aren't having fun), yet there's an odd sense of understanding and respect between them. They have secret gestures and codes that basically translate to, "I'm in the mood," and the other will accommodate. They also do it in a way that none of their friend group guesses they sleep with each other, because again: mutual hatred. It's complicated.

Another set of characters are happiest when they sit on the couch and read books together. Sometimes, they'll turn the page in the other's book for them, and it's so precious how in-sync they are with each other.

I once had a threesome that enjoyed riddle-speak. All three of them were kinky freaks (BDSM, with a dom, sub, and switch, and the dynamics were quite varied), but it was the riddles they told each other/answered that got them all flustered/turned-on/appreciative/etc.

Probably more, but those are my best examples.