Tying hubby to a chair and pulling a train for several of his friends.
OMG, I have so many! More than a few are hinted at on my page (feel free to enjoy them and comment on them).
Off the top of my head, I guess my filthiest would be hands handcuffed behind my back, ball gag around my neck, wearing skimpy transparent panties and an ass plug firmly seated. Then being dropped off at a frat party for the weekend with a sign around my neck saying, "Please pull up panties when pussy isn't in use." Those panties would be a gooey, smelly mess by midnight, but I'd be forced to wear them all weekend, feeling the mingled come of virile young men and my own juices squishing against my lips and ass.
With luck, I might reach the "hundred-man gangbang" ToshLoveCC talks about.