C’est un homme qui ne se laisse pas passer la plume par le bec = He is a man not easily taken in.
[Clerks bet a newcomer that he cannot write with a pen in his mouth. On his endeavouring to do so, they pull the pen sharply through his lips, thus inking his face. “Qu’on me fasse passer la plume par le bec.” Molière, Les Femmes Savantes, iii. 6.]
C’est un blanc bec = He is a beardless boy, greenhorn.
“Souffrez que je lui montre son bec jaune” = Allow me to show him he is a silly goose.
[Molière, Le Malade Imaginaire, iii. 17. Bec jaune or béjaune is an allusion to young birds whose beaks are generally yellow.]
Il a bec et ongles = He knows how to defend himself.
Avoir bon bec (fam.) = To be a chatterbox; To speak well; To be able to answer back.
[“Il n’est bon bec que de Paris” is the refrain of Villon’s “Ballade des Femmes de Paris.”]
Bécasse