Hi kamafight,
How about a estranged brother and sister who despise each other, being brought together to share and run a family business and share the family home, under the binding terms of their deceased parents Will.
The siblings are both very fit and physically strong, maybe the sister is a bodybuilder to even up the physical strength, the brother is gay and the sister is a lesbian. The sibling are very angry at being forced to live and work together and after much arguing and insulting over every single thing, the mudslinging over each other's sexuality pushes them over the edge and into physical confrontations which leave them both naked. After resuming their fight when naked, accidental penetration occurs which results in a full blown sexfight because neither will back down and be seen to be the one to "break" their coupling.
Sorry if this is too much to be allowed on this website