big mouth

/B IH1 G M AW0 TH/
noun
  1. 1

    The mouth of someone who talks too much, especially by making exaggerated claims or by inappropriately revealing information

    โ€œShut your big mouth or I'll shut it for you.โ€

  2. 2

    A person who talks too much, especially by making exaggerated claims or by inappropriately revealing information

    โ€œShut up, big mouth!โ€

Source: https://en.wiktionary.org/wiki/big%20mouth