“Bad girl! Let go of that!”
Your dog is chewing your shoe. You want to tell her to stop, so you angrily say this.
Bad girl! Let go of that!
Use this phrase when a pet, or a very young child, does something wrong. It's a simple, direct way of scolding them for misbehaving.
It's strange to use this with any people who are over about 3 years old. Once children are able to talk, you should use longer sentences to scold them.
If you do say "Bad boy!" or "Bad girl!" to an adult, it's usually within a joke, where you're pretending that the person is a baby or a pet.
To "let go of" something means to stop holding it. For example, if your child is grabbing your jacket while you walk down the street, and it's making it difficult for you to walk, you can say:
Let go of my Jacket, Aiden.
There's also another meaning of "let go of", which is to let go of something emotionally: