Howdy. I’m a native English speaker who also happens to have an English degree.

You can use a singular they in casual conversation. (I suppose Internet forums count as casual conversation.) “They are meeting us at the bar” is a perfectly acceptable thing to say if you are talking about meeting up with one person. It can be used regardless if you know the person’s sex or not. You can say a lot of weird casual things in English as a whole and many more depending on your dialect. Just two days ago, my fiancée was teasing me because I said “It needs popped” (in reference to my back). Omitting the “to be” is perfectly acceptable thing to do in my regional American dialect whereas it is not in her regional American dialect.

However, just because something can be used in casual spoken scenarios does not mean it’s appropriate in formal or written settings. I’d never walk into work and tell my boss something “needs signed.” My fiancée wouldn’t use any of the quirks of her dialect in a formal setting. (I’m omitting examples for her because she speaks a very distinctive dialect that essentially pinpoints us on a map.) Likewise, a singular they shouldn’t be used formal English or Standard Written English (SWE). It’s not only grammatically incorrect, but confusing to do so.

Another gaffe that comes up often is using they to refer to an individual as if he or she is a group. A sentence like, “If a child would like to participate in the class field trip, they will need a permission slip,” is incorrect. The correct usage is “he or she will need a permission slip” because you’re talking about requirements for individuals. The same thing applies for their. You’d say “If an employee has a concern, it is his or her right to contact Human Resources,” not “their right.” The genderspecials like to complain about the “he or she” and “his or hers” grammar rules, but any college entrance exam and any writing instructor will dock you for incorrect usage.

P.S. I apologize on behalf of all English speakers for our quirky language, especially our spelling. I can’t begin to imagine how frustrating it would be to learn this