It was a time when I was struggling with my OCD, and as this felt like enough trouble, I lightheartedly let go of social norms. I wore my hair mid-length (under a baseball hat; I am male), as the illness made it fairly difficult to groom it. I suppose my appearance, as well as my behavior, made me look kinda out of this world (although never displayed any overtly OCD behavior in front of the clerks in question).
I had recently gotten into the habit of shopping for meals at the meal stand at the local supermarket. The clerks at that stand were usually the same 2 women, maybe 30 years my senior. One of them (or maybe both) looked like they're stuck with a crappy life and are thus bitter, though they behaved normal on the surface.
Every day I went to that stand and said "Hi :) this-and-this meal, in a plastic bag please". I'm not sure how this sounds to english ears, but I said it in my native language, and it sounded fairly normal to me. In my language I didn't need to use the word "plastic"; it was implied.
The meals in that place are supposed to be taken home. The clerks put them in a flimsy, leaking plastic box for you, so if you don't take precautions, a big fraction of the time the meal (or at least its grease) gets smeared all over your other purchases as you carry it home. That's the reason I had taken to requesting my meal box to be put in one of the (small, free, tied) bags they usually use for sausages. I have no idea how common my request was, but I do know other clerks put the box into such a bag for me without me even having to ask.
On maybe the 10th or 15th day, I had only gotten to saying "this-and-this meal" and the older woman turned to the other, did an ugly grin and said in a hushed, mocking voice "...in a plastic bag please". The other woman joined her in her hushed mocking. I pretended I had not heard her, but I felt hurt.
Now, since I was not well mentally, I felt that if I came to that stand again, I would get intrusive thoughts about how they mocked me, and I would feel very awkward, since we both would know that they don't respect me.
I never went there again for maybe 3-4 years.
Now I'm glad to say my OCD is hardly present anymore, so I shop there again with little negative feelings.
But now I'm afraid that if something similar happens (in the 5 years since that incident, nothing of this magnitude has), I'll feel pressured and will again suppress all of my possible reactions, leading to bad feelings and future awkwardness.
Ideally, I'd like to learn some "social hack" to utilize in such situations, that lets me both maintain my dignity and not ruin my relationship with the rude person. So I don't want to report the rudeness to the store manager.
More recently (1 year ago) I had a similar incident in a gym, which I can describe on request. It ended badly for me.
To answer Anne Daunted's comment on my previous posting of this:
You want to know how to best respond when you order your meal in a plastic bag again and the clerk says to their colleague in a mocking way "... in a plastic bag please ..."? And you want to be polite? Else it's too broad.
I was aiming for a broader interpretation of the question, but since that's too broad, yes, your interpretation is acceptable. :)