When you rape a woman whereupon first raping her with fecal matter. Taking a shit into a girl's ass, then proceeding to rape her afterwards. Shit and all.
The Canadians are known for their mudslide as the asshole was often very cold during the winter, they needed a way of warming the opening for rape.
"I wanted to get my rape on, but it was so cold I had to perform a Canadian Mudslide."