“Hoy por ti, mañana por mí”
This Spanish saying refers to selfish social interaction: I do you a favor but I expect to have it returned in the future. The literal translation would be "Today for you, tomorrow for me". The saying "Today you, tomorrow me" can be used, but sparingly. The most widely used English equivalent is "Scratch my back, I'll scratch yours". By the way, in the English version the speaker asks for a favor before returning it.