scratch someone's back
Do someone a favor in hopes that a favor will be returned. For example, I don't mind driving this time—she's scratched my back plenty of times. It also is put as you scratch my back and I'll scratch yours, as in If you do the laundry I'll do the cooking—you scratch my back and I'll scratch yours. This idiom was first recorded in 1704.
Words nearby scratch someone's back
scratch hit,
scratch line,
scratch one's head,
scratch pad,
scratch sheet,
scratch someone's back,
scratch test,
scratch the surface,
scratch together,
scratch video,
scratch wig