Google "telling women to smile" (no quotes) should prove enlightening. If you want something more specific, I've provided two references in the post below.
I am of the opinion minor discomforts are things we have to deal with/adapt to. Especially when there is work to do. You seem to be of the opinion that personal discomforts are something that we should avoid causing as a matter of the upmost importance.
I think we have to agree to disagree.
It costs you nothing to not say something sexist to women. So it's pretty much a no-brainer to not say something sexist to them.
Why would you want to be the minor discomfort that people have to adapt to?
I just pointed out that you can choose to get offended by small stuff or you can just get on with things...
After all, someone saying "smile" to someone else really is small stuff.
Unless you actually have got someone fired for an innocuous comment. Then it's tough shit for them, I suppose.