Slightly misusing "thou" and "thee" to sound vaguely old-timey is both completely harmless and irrationally maddening to me, especially in kink spaces where language that reinforces closeness or dominance has so much potential.
Firstly, "thou" is a subject, "thee" is an object and "thy" is possessive. These get mixed up pretty often. I don't consciously diagram the grammar of every sentence, but if you read or hear enough early modern English it can eventually feel natural.
"Thou" is an "informal you," a second person pronoun that implies familiarity. It either communicates a degree of closeness or reinforces your status above someone in a hierarchy. "Thou" is for close friends, lovers, children, commoners and servants.
My main gripe with "ye olde timey" styling is just that knightposting using an "informal you" to sound vaguely historical is completely missing out on the opportunity to use "thee" and "thou" to imply an inappropriately close relationship, or a flipped power dynamic.
A few other things I think we're under utilizing in royalty kink:
I have never seen the word "sirrah" in a kink setting, but it could translate beautifully into D/s dynamics. "Sirrah" is the opposite of "sir," a title reserved for someone who is below you. It's a fantastic word for when you want to put someone in their place, and sound a bit grandiose and archaic in the process. It's also very fun to say.
"Thy Grace" or "Thy Highness" would be grammatically incorrect and paradoxical, making them the perfect stylings for a submissive royal.
For a non-binary knight or other nobility, in place of "sir" or "lady," might I suggest "noble" and "gentle" as possible gender-neutral titles?
In a similar vein, I have heard so many people struggling to find a gender neutral way to say "ladies and gentlemen" or "lords and ladies," and I would suggest "nobles," "gentles," "gentlefolk," and "gentle people" as alternatives.
