scratch one's back

scratch one's back  {v. phr.},  {informal}
To do something kind and helpful for someone or to flatter him in the hope that he will do something for you. Usually used in the expression "You scratch my back and I'll scratch yours."
Mary asked Jean to introduce her to her brother. Jean said, "You scratch my back and I'll scratch yours."
Categories: {informal} {v. phr.}