Il a les jambes en manche de veste (fam.) = He is bow-legged.
Il le fera par dessous la jambe = He will do it with the greatest ease (or, carelessly).
Il a des fourmis dans les jambes = He is fidgety, restless.
Jaune
Jaune comme un coing = As yellow as a guinea.
Jean
Être gros Jean comme devant = To be no better off than one was before, in spite of all one’s efforts.
[Rabelais, Pantagruel, iv. second prologue, and La Fontaine, Fables, vii. 10.]
Jeter
Il jette son argent par les fenêtres = He plays ducks and drakes with his money.