What is a grimy mitt?

A "grimy mitt" is a slang term for a dirty oven mitt. It's used to describe the mitt's appearance after being used repeatedly to handle hot items in the kitchen.

The term "grimy" suggests that the mitt is covered in a layer of grease, food particles, and other kitchen debris.

So, if someone is talking about a "grimy mitt," they are referring to an oven mitt that needs a good cleaning.