What's "full of it" mean here?

Native speaker’s answer
Rebecca
To be "full of it" is an informal expression used when you want to say that a person is talking nonsense, is unreliable, or is overly confident or boastful. Ex: I don't like that dude. He's so full of it, boasting about things all the time. Ex: He's so full of it. Nothing he says is ever true.