“May your hand not hurt.”

Thank you, for a meal, a favour or any effort someone has made for you.

Heard in the wild

چه غذای خوشمزه‌ای! دستت درد نکنه.

What a delicious meal. Thank you so much!

A note

The polite reply is sar-et dard nakone: may your head not hurt.

More people and manners

خسته نباشید
khaste nabâshid
“May you not be tired.”
A greeting that acknowledges someone's work, said to shopkeepers, teachers or anyone at the end of an effort, whether or not they look tired.
قابل نداره
ghâbel nadâre
“It isn't worthy of you.”
Classic taarof: a shopkeeper or host politely waves away payment or thanks, and you are expected to insist.
به روی چشم
be ru-ye cheshm
“On my eyes.”
Gladly, consider it done. Even a simple cheshm, "eye", means "yes, will do".
چشمتون روشن
cheshmetun roshan
“May your eyes be bright.”
Congratulations on the arrival or return of someone dear: a new baby, or a relative home from abroad.