The Mud-Onion Salad Toss is a sexual act in which both partners make, and then mix, their shit together. One will then hand wank the other to completion with as much shit-mix on their hands as possible.
"Sorry if you can smell runny onions, lads. I was on that Mud-Onion Salad hype last night and didn't get a thorough scrub in this morning."
"Ever since that Mud-Onion Salad Toss, my dick skin has been silken and smooth!"