The fun French idiom “Être soupe au lait” translates directly to “to be milk soup”and really means is to be hotheaded or quick to anger. Grammatically, soupe au lait is used as an adjective. French-to-French translations include impétueux, impulsif and sanguin, which all translate to hotheaded.
être soupe au lait
to be hotheaded, quick to angery

According to Linternaute.fr, the expression soupe au lait first appeared in the 19th century. It’s a metaphor for warming milk, which comes a boil suddenly. The sudden boiling of the milk represents sudden anger or changes in mood.
Here are two example sentences of the idiom.
Papa est tellement soupe au lait, il s’énerve toujours pour rien.
Dad has such a short fuse. He always gets angry over nothing.
Pourquoi est-ce que tu te mets en colère sans provocation ? Tu es vraiment soupe au lait !
Why to you get angry with provocation? You’re really get angry easily.
Conclusion
Et voilà ! You now know how to use the French idiom soupe au lait. Now check out our other fun idiom posts including tomber dans les pommes (to faint), avoir le cafard (to feel depressed) and être dans la lune (to be absent minded)
