i cut my own slack - A selfish way of saying you don’t need anyone else, because

A selfish way of saying you don’t need anyone else, because you're too good for them, and you’d rather do it yourself.

I cut my own slack. You're still arguing with your friend, and I already finished my homework and got my snack.

I cut my own slack. You're still waiting for your brother to help you, and I already finished my math and got my candy.

I cut my own slack. You're still fighting with your sister, and I already finished my work and had my lunch.