In "who left their bag here"'s case, the gender of the person is not known because their identity isn't known, so it doesn't feel strange to use (for us old farts). It can take some effort to retrain your brain to use "they" when it's a single person whose identity is known (speaking from experience as a Gen Xer).
Or the person might just be a transphobic asshole. But I like to think that most just need to educate themselves on using pronouns correctly.
When I started interacting with a non-binary person more often, the only reflexive pronoun that came to mind was ‘themselves.’ As in, “They bought themselves a pair of socks for their birthday.” It felt a bit awkward since I couldn’t shake the plural association in my head, but I still used it to be respectful.
Then I remembered that the word ‘themself’ exists and I felt stupid.
Calling people what they ask to be called just doesn't have to be this difficult.
And yes, his royal lordship Starn, the majestic, that goes for you, too. It's fine. We're cool with your chosen name. And I admit, the opera cape absolutely works for you.
And I don't need to know what genitalia most other people are rocking. That's none of my business, unless we're really into each-other, in a very intimate way.
It takes all my willpower not to be get pretty inappropriate every time a government form asks my birth sex:
"Oh! We just met at this office of motor vehicles...I didn't know you felt that way about me! This is so much to process. I admit there's a mutual attraction. Of course I feel it too. I'm delighted that you had a special form made up to ask! I'm flattered! Want to grab dinner, and see where this goes?"
In Finnish language there are no gender specific pronouns only gender neutral one hän/hänen.
They/them still sounds weird to use even if I know it can be used to refer single person. When talking or writing fast I'll still often accidentally default to using he/him even for females which I then have to correct.
Dear native English speakers, would you mind inventing a new word either for gender-neutral third-person singular pronoun, or one for what "they" mean to foreign English speakers since you are so insisted in differing its meaning from the text books you shipped us decades ago?
English is so inconsistent at this point. Only the third-person pronouns have gender in singular form, the plural form has no gender and now you are telling us the gender-less form can be singular now? How confusing!
English is widespread partly because it has simple alphabet and relatively easy grammar. I don't mind someone being in LGBT+ group at all, but could you please don't mess with the language?