|cornichon nm||familier (imbécile) (informal, pejorative)||nitwit n|
|Martine l'injurie et le traite de cornichon.|
|Martine insults him and treats him like a nitwit.|
"treats him like a nitwit" or "calls him a nitwit"?
(let's note that "cornichon" is rather mild, dated and would mostly be heard in schoolyards of the 1960s (not that I was there, but I wouldn't be surprised to find it in Le Petit Nicolas).