From Wiktionary, the free dictionary
έλα παππού μου, να σου δείξω τ' αμπελοχώραφά σου • (éla pappoú mou, na sou deíxo t' ampelochórafá sou) ("Come here grandpa so I can show you your vineyards")
- (sarcastic) teach grandma how to suck eggs (telling an expert how to do things)