1) Mom vs her daughter's lesbian girlfriend who just made a pass at mom.
2) Young woman (20's) vs a new roommate (who turns out to have 'designs' on her)
3) Step-mom vs step-daughter over... anything. (insert a favorite cliché here)
4) Mom vs her daughter's new step-mom (after a bitter divorce!) w/daughter watching.
5) Step-mom vs her TWO new step-daughters (twice the daughters = twice the fun!)
6) Country cousins vs City cousins (I seriously doubt this has EVER been done - OK, maybe a million times, but still - with muddy fields, cow pies, cutoff jeans, blouses tied up under heaving 'corn fed' blonde bosoms.... it's considered "timeless" by experts in the field).
7) My personal favorite. A redheaded fight story writer (of a 'certain age') vs a young upstart who has "stolen" the idea for her latest "erotic adult themed novel" and posted it on an Internet bulletin board....
(ANY of these would/could involve interracial pairings....Black; White; Asian; Latina; or different nationalities, hair colors, or socio-economic strata. I leave those decisions to the author(ess).)