If someone has a big mouth, he/she is actually loudmouthed and gossipy. A person who cannot keep a secret can also be regarded as a big mouth. 在俚语中，big mouth指喋喋不休、乱嚼舌头的人。 要特别注意，“把你的嘴张开”要说成“open your mouth wide”，而不能说成“open your big mouth”噢！

Examples:
You talk a lot about other people’s business. You have such a big mouth. 你说了这么多别人的事情。你真是个多嘴的人！

You have a big mouth. Leave me alone. 你总是喋喋不休的。走开，别理我！