Cracher dans la soupe is a French expression that translates literally to “to spit in the soup” and means “to bite the hand that feeds you” or “to be ungrateful towards somebody you depend on”.
Cracher dans la soupe
to bite the hand that feeds you

Expression origin
In the past, soup was considered to be indispensable. Thus, spitting in the soup meant to refuse something perceived as beneficial.
Example sentences
Quand on t’offre un nouvel emploi il ne faut jamais cracher dans la soupe.
Never bite the hand that feeds you when you’re offered a new job.
Il a accepté le poste parce qu’il était jeune et il ne voulait pas cracher dans la soupe.
He accepted the job position because he was young and didn’t want to bite the hand that feeds him.