We use this expression to say thank you for something and say that maybe the other person has been too generous.
You can use this phrase in ………… language.
A: Hey, everyone, I’ve bought champagne. There is enough for everybody.
B: Thanks Michal. Really you shouldn’t have.
A: Don’t mention it.
A: Simon, I’m speechless. This is a real diamond ring.
B: Well I wanted to get something you’d like and …
A: I do. It’s perfect. But really, you shouldn’t have.