French phrase
Vraiment, vous n'auriez pas dû.
Meaning
Really, you shouldn't have.
When to use it
A polite expression of thanks for someone's kindness. It is used when someone has gone to trouble for another person and sounds modest and appreciative.
Example dialogue
J'ai réglé l'addition.
I paid the bill.
Vraiment, vous n'auriez pas dû. Merci beaucoup.
Really, you shouldn't have. Thank you very much.