When a man takes a firm shit and uses a cheese grater to grind it over a woman's face. The man may then proceed to ejaculate on top as icing on the cake.
A "Cheese Grater" is someone of incredibly low inteligence. The term Cheese Grater comes from the belief that all inteligent people start with a base I.Q. Like cheese (you start with so much), and these imbeciles come along and shred every precious point from you; simmilarly to how one grates a cheese block.
Teacher: Melissa, explain to me the importance of Planck's Constant.
Melissa: What did you say? Are you talking to me? Cause, um like I'm in the middle of texting some important people , duh.