big mouth

noun2

1. •
   (disapproving) The mouth of someone who talks too much, especially by making exaggerated claims or by inappropriately revealing information.

   • Shut your big mouth or I'll shut it for you.
2. •
   (disapproving) A person who talks too much, especially by making exaggerated claims or by inappropriately revealing information.

   • Shut up, big mouth!