Don't say 笨 yourself. Don't be afraid!

You can just say: "I am offended by what you said. Don't you know you have been very impolite to me?" with firm and be strong voice. If she acts it again after you *push* her back, you may just tell her that you will have to talk to your HR.

Once my boss was very impolite to me, I *pushed* him back. He was very surprised. Since then he's been very nice to me. In fact I'm the only girl in my group,he treats me faire. My hubby told me I should say back ALWAYS if I am offended. Here is America!