I'm wearing cute little flowery gym or yoga pants (or a bit like jammies really) and I'm going to mess them up real good! I'm gonna wet myself and do a big shit in them. Does the thought of that make you hard?
First my poop is all runny and flows down one of my legs, but then I start pushing out a big firmer load, which makes a sexy poop bulge in the back of my pants, before falling down a bit inside them and just hanging there, a giant pile of poop hanging in my pants between my legs.
Then, with my pants totally loaded, I begin to wet myself. Piss flows everywhere and mixes with the poop, loosening the big bulge so it falls all the way down my leg and onto the floor. As I continue to pee I let out a long series of squelchy farts and a bit more poop, until my pants are just a completely filthy wet and dirty mess!