I found the lines in Juvenal,
Satire VII, 50-52:
nam si discedas, laqueo tenet ambitiosi
consuetudo mali, tenet insanabile multos
scribendi cacoethes et aegro in corde senescit.
These and surrounding lines translated by Peter Green:
You can't
escape you're caught in the noose of bad ambitious
habit; there are so many possessed by an
incurable
endemic writer's itch that becomes a sick obsession.
But the outstanding poet, one who mines no common seam,
smelts down no reworked slag, strikes no debased
poetic currency, minted with populist platitudes--
I can't hink of one just now, still I'm sure they exist--
Etymology is kakos/Greek= "bad" and ethos/Greek="character/dispostion" so "the bad disposition to write" [scribendi/Latin/write]. It's odd but I always had the feeling that it meant a "shit eating writer" but I'm too lazy now to look up whether English slang "ca-ca" for shit is related to Greek "kakos" for "bad". It may be. OK. There's a thread somewhere where someone mentions that Kenneth Rexroth was called Cacoethes in Kerouac's
Dharma Bums so there's another interesting connection
Ola, Cirerita! und wie gehts Johannes in Osterreich? Here is a scan of Cacoethes Scibendi. Cheers!