There's two ways to go about it...
The first way is to write fan fiction inspired by old exploitation films and B-movies/Z-movies, often AU stories set in the typical grindhouse film genres (martial arts, cannibal horror, zombies, outlaw biker stories, splatter-punk, Spaghetti Western, Blaxploitation, fanservice stories, etc.)
The second way is to write deliberate "bad fic" in a sense, but not blatantly obvious bad fic, so you're not going to see the wacky troll fic stuff from guys like ShakespeareHemmingway or works like My Immortal
This second way involves common tropes and genres in fan fiction that are viewed with utter cringe such as AU fics or Self-Inserts and play them so straight that they end up becoming a subtle parody or at least a fun throwback to a simpler time in fandom history when you could just write dumb fan fic and not be dragged into political nonsense
The Fandom Grindhouse will have both types of fan fiction, of course.
I guess you could call this thing "Fansploitation" or something like that.