Sometime after the Cell Saga, Yamcha and 17 hit it off and start dating. Bulma throws a party and invites (read: blackmails) everyone into coming. 17 and Yamcha go as a couple and much awkwardness, fluff, hilarity and trolling on Bulma's part ensue. (I think she's tease Yamcha about this, but not in a mean way.) Bonus points for 18 not-so-subtly investigating Yamcha to figure out if he's worthy of her little brother.

Yeah, I know it's not kinky, but you can write smut or not.