Don’t dignify insult with reply

Dear Miss Manners: I was standing in the checkout line at a convenience store when I heard a male voice behind me say, “I’m the fashion police, and those pants don’t flatter you.”
I turned around to find a somewhat disheveled-looking man who didn’t look like a fashion plate himself. I tried to make light of the situation, but he wouldn’t give up.
When I said I was in a hurry that morning and settled on the slacks since they didn’t require ironing, he told me to get up earlier tomorrow so I could iron. Then, as I left the store, he yelled, “Throw those pants in the Dumpster!”
I’ll admit that my slacks are a bit loose, as I’ve lost weight recently. However, it doesn’t seem to me that it’s any of his business, and I’m irritated by the thought that he was staring at my backside and found a need to voice his displeasure. What would have been the appropriate response to discourage further comments?
Gentle Reader: Miss Manners is afraid that it would be as rude to go around vilifying people for their manners as for their clothing. It would also be as ineffective as your “light banter,” and not only because Miss Manners refuses to go around like a meter maid, issuing tickets on the street.
To reply to such an insult is to admit the right of the stranger to make it, arguing only about whether the content was fair. Your first reaction should be to turn away and ignore the remark. If that fails to stop this outrageous intrusion, it will be time to say, “Please stop harassing me,” and perhaps to add, “or I will have to call the real police.”
Dear Miss Manners: I have social anxiety disorder, meaning I feel uncomfortable and anxious among other people, to the extent that I sometimes don’t even want to enter a room in which my parents are (I am 34 years old). I am seeing a therapist and do realize that it is unreasonable, but that’s the way I am and probably will be for the rest of my life.
But my problem is this. Sometimes when I am with other people and the anxiety takes over, I freeze completely and want to withdraw. I need to be alone for a while just to recover my wits and relax.
What can I say to people – something like “You’re freaking me out, I am leaving” – without hurting their feelings?
Gentle Reader: Not anything remotely like, “You’re freaking me out. I am leaving.”
Not only is there no way that this can be made to sound polite, but it explains – erroneously – what the problem is. The other people may trigger your problem, but they did not cause it.
Yet Miss Manners agrees that you need not offer a full explanation. You need only say, “Excuse me. I’m not feeling well,” adding, to ward off inquiry, “but it’s nothing; I’ll be all right shortly.”