That exact phrase occurs in a bunch of places. IMDB has it in a Voltron episode a decade before The Lion King.
132 is the rudest number.I don't absolutely know this to be the case beyond a shadow of a doubt, but I'd be very surprised if the first recorded use of the phrase was in something so recent as Voltron. More likely it dates back to the '30s, or even to The Zeroth Law Of Trope Examples.
Jet-a-Reeno!I didn't even know "jackasses" was a slang back in 1902. o.o
Anyway, I guess this suggests it's hard to find out what the Trope Codifier was... but for Stock Phrases does a Trope Namer have to correspond with that? I recall in YKTTW using "Trope Namer" for wordings that didn't originate with the examples I used, is it improper to use Trope Namer that way?
Stock Phrases don't really have a Trope Namer as such. The name of the trope is the phrase — it's not named after anything.
Well, there could be a Trope Codifier such that the other uses of the Stock Phrase could be in reference to a particular use. That's what I was referring to.
Oh, there could be a Trope Codifier for a Stock Phrase, certainly. Airplane is probably the Codifier for "Picked a bad day to stop <verbing>", and Bela Lugosi in Dracula is the codifier for "I never <verb> ...[pause]... <noun>."
Neo, #8: Your comment made me curious so I looked up the etymology. The earliest attested use of "jackass" to mean "a stupid person" is from 1823. In this case, "attested" means "a written work that uses it that way has been identified. It may be in a still older work, but if it is, no one has let the OED know yet.

Surrounded by Idiots
Scar says this verbatim about his hyena minions. Given that the movie he's from is one of the most well-known Disney movies ever, I'm kind of left wondering if he named the trope, but I did ctrl+F of trope namer on the examples list, and ctrl+F of Lion King on the Trope Namers list, and got nothing.
On a sidenote, why aren't trope namers organized by tropes instead?