Shitnuts is the act of a man inserting his testicles into his partner's anus, specifically a dirty one. When the scrotum comes out, it should be covered in shit.
Greg: Man, I heard you tried shitnuts with Bianca last night Tom: Yeah, so what? I like the creamy feeling.
Greg: Tom, that's absolutely foul.
1. An interjection used to say something you have earned, lost, forgotten, completed, etc.
2. Funny word that takes the place of "shit." Usually makes other people laugh, and also is legit to use in school.