Translated it to "fiend" instead of just "alien" to still carry the slang meaning and added that "fiendish" at the start, so we know that she's still talking about aliens when she says "boob fiend." But you already knew that. lol
Now even though its origins are unclear, oppai seijin apparently started out meaning someone who likes boobs, then it turned to mean someone who likes big boobs. There's also the interpretation of it referring to someone who has big boobs. And after those, the term was generalized, with "X-seijin" meaning "someone who really loves X." That's pretty much it from what I found on Japanese Wikipedia.
Next, the term Mikurube uses when referring to the ghost clinging onto Irosaki is 取り憑く (toritsuku), even back in Chapter 23.
While this means "to possess," it can simply mean "to haunt," which is the more accurate translation for what's actually happening to sensei. Apologies for the oversight. Ch. 23's been updated now too.
And, as always, let me know of any errors or points of improvement here in the forums. Thanks
