Alors, oui, est-ce une personne qui a "la langue bien pendue", qui a "perdu sa langue", qui donne "sa langue au chat", qui est tout simplement "une mauvaise langue" ou un bavard (ou "buvard") invétéré qui ne sait pas la tenir cette langue ? Eh bien, c'est...

= Be as thick as thieves. Ex. At the beginning, they didn't like each other. But after a few hours, they were as thick as thieves.