TL;DR, most people are reasonable and can tell the difference. We cool.

People where English is not their first language get a pass. There is usually a very telling inflection when someone says "females" and means it in the bad way. I would rather help people with their English and explain that it is best to not say it that way, than get upset over our language being unnecessarily complicated.

The context of how female is said is even more confusing. Best way I think is if you are referring to a group of people or a specific person as female(s), that is bad. If you are referring to something about our gender, a description, or something impersonal, then that is fine. "Female anatomy.", "I hate being female.", "There was a female guard at the station."

While it is puts me on edge when I hear it (in that bad context), it isn't like they called me a cunt or something really foul. It is usually just an immediate red flag that we may be dealing with an incel, but let's see where this goes. Usually doesn't take long to get a confirmation on how they really meant it.