The benefit to dating a guy who regularly gets splattered and caked in mud is you never have to buy him a spa gift certificate. Though I'm thinking spa-grade mud is of a bit different quality than random sludge.
But when you're getting a mud treatment at a spa, they tend to dissuade boners.
Now I can't recreate the sound effects of all this. The squishes and splashes and splorks and squeaks and sucks. But I'm assuming that's part of the kink. As the mud is its own organism at that point.
As it dries and caresses the body, it's like a gentle, insistent hand. As it pulls the body into it, creating a vacuum that won't let go easily, it's a needy, tender lover. As it makes bodies slip and smash and glide along each other, it's organic lubricant.
Or it's just guys who like to get deeply messy as they do their best impression of a background actor in a beer commercial. Not all of these are sexual situations but if you're into this kind of thing, then even the nonsexual ones are pretty damn sexual.
Meanwhile, the real victor in all of this are laundry detergent companies. Except for advanced cases where guys don't emotionally soil their experience by ever washing their clothes. That would be filthy.