All Bark and No Bite

Expression: "all bark and no bite"

Meaning: This idiom originated with dogs, the type that bark loudly and may seem scary, but they don't actually attack. Over time this expression has evolved to refer to people, who obviously don't bark like dogs, but they talk tough and make threats that they don't actually follow through on.

Example: "He threatened to punch me in my face, but he's all bark and no bite."