A sloppy casserole involves three people. Preferably two girls and one gentleman. The casserole consists of feces, menstruation, and seminal fluids. They are combined on the chest of one of the ladies. It's sloppy because of the incredible mess it creates.
"Clint once gave a sloppy casserole to this chick I heard." - Rynoceros
"No way, are there leftovers?" - Ryan