小事一桩

That's a piece of cake

That's as easy as pie!

I can do it with my eyes closed

请你客气点

Who do you think you're talking to?

Don't get fresh with me (get fresh with 大多用于母亲对孩子的斥责之时)

等着瞧

you'll see

Time will tell

多管闲事

(It is) None of your business

Mind your won business

Who asked you?

This has nothing to do with you