English is definitely one of the least sexualizing languages of the Romance Languages. In French or Spanish, everything would be attached to a gender, but that doesn't mean that the words define the gender themselves. Nobody in Spain thinks that chairs are 'where women belong' or anything like that.
I don't necessarily think that response is justified when no offense is actually meant. But the point is that there has been an identifiable trend in our language towards moving away from gender-specific terms for roles that shouldn't otherwise have a relevance to gender.
I'd argue this movement is overdue for epithets. I think "asshole," "asshat," "assclown," really anything in the venerable ass family, makes for an ideal gender-neutral epithet. We should use these more often!
Edit: typo
So a sincere question: Why would someone be offended to be described as a waitress?
I find server to refer to a waitress and waiter a really odd term, almost de-humanising but that might just be a cultural difference.
Most of the French grammar bits have been discarded in quotidian speech long ago; how often do you hear the subjunctive voice used in English?
English is distinct from other Germanic languages, though, in the same way. Most European languages of any stripe are gender-heavy while English mostly applies grammatical gender mostly only to vehicles and individual sexually dimorphic animals.
It's more productive not to muddy the waters though: it's not like there are only a handful of ways to insult someone.