be no skin off (one's) back
To be no cause of concern or interest to one; to pose one no difficulty, threat, or risk. Hey, it's no skin off my back if you want to get a tattoo. I'm just saying that it's something you may regret someday. We all knew that the head chef was stealing from the kitchen, but it was no skin off our backs so we just kept our mouths shut. A: "Do you mind if I store some of my stuff in your garage for a while?" B: "Eh, it's no skin off my back."