Oh no, we're going to be able to win free dog related products?! Who are these awful corporate people??
Anyhow, I'll retell my favorite Smalls tale, which is usually designed to scare folks away from puppies.

I don't know if we're looking for GROSSEST, but with her gross is all I have to work with.
When I picked up Smalls from the shelter, she was a 5 week old stray. She had a prolapsed rectum and ruptured intestines that were surgically corrected the second I got her. It was a rough surgery that she wasn't supposed to survived and left her with a chunk of missing intestines and the remaining intestines were tacked. She wouldn't be able to go to the bathroom for a few days with the swelling, but she tried constantly (which I had to interrupt so she wouldn't strain). I'm a big pushover and let her sleep on the floor in a little bedding area I made her, so I could have my arm off the side of the bed (which was only a foot or so off the ground) to comfort her through out the night.
I thought she could not get onto the bed and thus was cordoned off from the room. I learned this was wrong when she not only jumped onto the bed, but her flood gates opened all over my pillow. I woke up with bloody diarrhea all over my face and head- and I sleep with my mouth open.
Can that thing catch those kind of incidents?

She also pooped an entire turd ON the wall. It looked like she had backed right up and pooped. It is a shame I lost the photo. We took a picture of it and photo shopped it to look like a framed painting on our wall.