The most important thing, then, is to get introductions out of the way first, so we don't have to continue saying "the girl who looked like string cheese waved at the boy who was wearing his glasses upside-down". There's really no better way to go about things unfortunately, unless you like your characters to be omniscient. :p
*shrugs* Depends on how you want your writing to be.
Sometimes, if my character doesn't know another character's name, then I'll refer to them based on a description like the example you just gave. Other times, if I decide that it's just not worth bothering with, I'll go ahead and throw the character's name in, even if my character doesn't know it. Besides, it's not like my character
said their name -- I only included the name in the narration because sometimes that makes things easier for the reader
(or writer). 3rd person omniscient is a thing -- and it doesn't mean your character is omniscient. :P The trouble is that RP posts are
usually written in 3rd person limited, but it's not
too uncommon for the narration of a post to include information that the character doesn't know (which, again, is different from your
character knowing that information that they shouldn't, because that would be metagaming). So really, RP posts tend to flip-flop a lot between 3rd person limited and 3rd person omniscient (usually leaning more towards the former than the latter, though).
So if you want to be really strict about your consistency in sticking to 3rd person limited, then, yeah, I see your point. But I know
I'm not always consistent about it and I really don't care. ¯\_(ツ)_/¯ I care more about function than form when it comes to this kind of stuff.