A:I think you should dye your hair green. B:(żartujesz sobie), right?
you're kidding/you're joking
A: I'm going out tonight. What should I wear? B: (Dlaczego nie założysz) this dress?
Why don't you wear
A: You shouldn't go there. It's dangerous. B: (Dzięki za radę)
Thanks for the advice.