I agree that smiling at a rude person could pull the rug from under them. But, I have to admit, when in that situation, the last thing I can do is smile. I think my face would crack.

I used to cower if someone was rude. I was often so taken a back, I just didn't know what to say. But over the years, I have developed a protective shield around me. If I don't like something, I let that person know...not to discipline his/her bad mouth; but to make me feel good.
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As soon as you trust yourself, you will know how to live.
Goethe