Galen does not like Archigenes' jargon

"The next thing Archigenes says, i.e., 'when there is a narrowing, the nerves have "full pains",' he said using affectatious language. It explains nothing more than what comes after it, where he says the pains are 'least diffuse'."

Tὸ δ’ ἐφεξῆς εἰρημένον ὑπὸ τοῦ Ἀρχιγένους, ὅτι καὶ στενοχωρίας πλήρεις ἔχει τὰ νεῦρα τοὺς πόνους, κακοζήλως μὲν εἴρηται τῇ λέξει. δηλοῖ δ’ οὐδὲν πλέον τοῦ μετ’ αὐτό, καθ’ ὅ φησι καὶ ἥκιστα κεχυμένους.

Galen, De locis affectis II 8,15 (CMG V 6,1,1 340,12-14 Gärtner = VIII 100 K)

'κακοζηλία' - comes from rhetoric. The adjective seems to have been floating around for a while, but at some point it was appropriated (perhaps by pseudo-Demetrius) to describe bad style in speech. It's usually translated, 'affectation', although I find that doesn't really capture it. In a strict sense, kakozêlia means "a zeal for all that is bad": it describes any expression which exceeds the boundaries of eloquence and passes into the absurd. There are a few nice examples in pseudo-Demetrius (below). Lucian seems to have extended it to describe over-acting. Hermogenes gives a summary explanation of what it is about affectation we find so wrong. And there's a discussion of it in Quintillian, Institutio Oratoria 8.3.56, which I'm leaving out. All these writers seem to agree that affectation causes an expression to fail. The tension it causes between the seriousness of the author's intent and the silliness or baseness of their execution ends up making the result seem too implausible to be taken seriously.

Pseudo-Demetrius

"186. [...] Just as the frigid style is closely connected to the magnificent, so there is a certain defective style closely connected with the refined. Following the colloquial expression, I call it "affectation" (kakozelon). Like all the other styles, it occurs in three aspects of style.

187. In thought, like the guy who talked about "the Centaur riding itself", or, that time Alexander wanted to compete in a race at the Olympics, and someone said, "Alexander, run along the name of your mother!"

188. It occurs in words as, for example, "somewhere, a sweet-faced rose was laughing": the 'laughing' metaphor is out of place and does not fit at all, and the compound 'sweet-faced' – no one of sound judgment would put that in a poem. Another example is someone who once said, "the pine was whistling at the gentle breeze." But enough about diction.

189. The composition, e.g. the anapaestic and especially those resembling lamentable and undignified meters, like the Sotadean one, because of its softness: "after searching in the burning heat, cover up" and "waving the spear of Ash Pelian to the right over his shoulder", instead of "waving the Pelian spear of Ash over his right shoulder." The line seems transformed somehow, like those who the fables tell us transform from men into women. So much concerning affectation."

186. [...] καθάπερ δὲ τῷ μεγαλοπρεπεῖ παρέκειτο ὁ ψυχρὸς χαρακτήρ, οὕτως τῷ γλαφυρῷ παράκειταί τις διημαρτημένος. ὀνομάζω δὲ αὐτὸν τῷ κοινῷ ὀνόματι κακόζηλον. γίνεται δ' αὖ καὶ οὗτος ἐν τρισίν, ὥσπερ καὶ οἱ λοιποὶ πάντες.

187. Ἐν διανοίᾳ μέν, ὡς ὁ εἰπὼν «Κένταυρος ἑαυτὸν ἱππεύων», καὶ ἐπὶ τοῦ βουλευομένου Ἀλεξάνδρου δρόμον ἀγωνίσασθαι Ὀλυμπίασιν ἔφη τις οὕτως· «Ἀλέξανδρε, δράμε σου τῆς μητρὸς τὸ ὄνομα».

188. Ἐν δὲ ὀνόμασιν γίγνοιτ' ἂν οὕτως, οἷον «ἐγέλα που ῥόδον ἡδύχροον»· ἥ τε γὰρ μεταφορὰ ἡ ἐγέλα πάνυ μετάκειται ἀπρεπῶς, καὶ τὸ σύνθετον τὸ ἡδύχροον οὐδ' ἐν ποιήματι θείη ἄν τις ἀκριβῶς σωφρονῶν. ἢ ὥς τις εἶπεν, ὅτι· «λεπταῖς ὑπεσύριζε πίτυς αὔραις»· περὶ μὲν δὴ τὴν λέξιν οὕτως.

189. Σύνθεσις δὲ †ἀναπαιστικὴ καὶ μάλιστα ἐοικυῖα τοῖς κεκλασμένοις καὶ ἀσέμνοις μέτροις, οἷα μάλιστα τὰ Σωτάδεια διὰ τὸ μαλακώτερον· «σκήλας καύματι κάλυψον», καὶ «σείων μελίην Πηλιάδα δεξιὸν κατ' ὦμον» ἀντὶ τοῦ «σείων Πηλιάδα μελίην κατὰ δεξιὸν ὦμον»· ὁποῖα γὰρ μεταμεμορφωμένῳ ἔοικεν ὁ στίχος, ὥσπερ οἱ μυθευόμενοι ἐξ ἀρρένων μεταβαλεῖν εἰς θηλείας. τοσάδε μὲν καὶ περὶ κακοζηλίας.

Demetrius [sp.?], De elocutione 3.186-189 (156,5-158,3 Rhys Roberts)

Lucian

"Just as in rhetoric, so in pantomime there can be, to use the popular phrase, "affectation", when an actor goes beyond the appropriate measure of the performance and exceeds the limit of what is required. For example, if one needs represent something great, what is performed is something monstrously big; if soft, by exaggeration it becomes effeminate; and manliness is raised up to wildness and beastliness."

Γίνεται δέ, ὥσπερ ἐν λόγοις, οὕτω δὲ καὶ ἐν ὀρχήσει ἡ πρὸς τῶν πολλῶν λεγομένη κακοζηλία ὑπερβαινόντων τὸ μέτρον τῆς μιμήσεως καὶ πέρα τοῦ δέοντος ἐπιτεινόντων, καὶ εἰ μέγα τι δεῖξαι δέοι, ὑπερμέγεθες ἐπιδεικνυμένων, καὶ εἰ ἁπαλόν, καθ' ὑπερβολὴν θηλυνομένων, καὶ τὰ ἀνδρώδη ἄχρι τοῦ ἀγρίου καὶ θηριώδους προαγόντων.

Lucian, De saltatione, §82 (ed. Harmon, Cambridge, Mass., 1936)

Hermogenes

"An expression becomes 'affected' either by what is impossible, inconsistent (i.e., incompatible), base, sacrilegious, unjust, or contrary to nature – those styles that cause us to dismiss a story and toss it out because it is incredible. In fact, this is why we say a piece is successful as long as it is likely, since when something is found to go beyond what is likely, it always ends up being in bad taste and dismissed. In these cases, we say 'this is not likely to have happened', either because it is impossible, or because it is shameful, etc."

Τὸ δὲ κακόζηλον γίνεται ἢ κατὰ τὸ ἀδύνατον ἢ κατὰ τὸ ἀνακόλουθον, ὃ καὶ ἐναντίωμά ἐστιν, ἢ κατὰ τὸ αἰσχρὸν ἢ κατὰ τὸ ἀσεβὲς ἢ κατὰ τὸ ἄδικον ἢ κατὰ τὸ τῇ φύσει πολέμιον, καθ' οὓς τρόπους καὶ ἀνασκευάζομεν μάλιστα τὰ διηγήματα ἐκβάλλοντες ὡς ἄπιστα. Διά τοι τοῦτό φαμεν καὶ τὰς διασκευὰς μέχρι τοῦ εἰκότος προχωρεῖν, ὡς, εἰ παρὰ τὸ εἰκὸς εὑρεθείη τι, πάντως καὶ κακόζηλον ἐσόμενον καὶ ἐμπεσούμενον τῇ ἀνασκευῇ· καὶ γὰρ ἐκεῖ λέγομεν ‘οὐκ εἰκὸς τόδε πραχθῆναι’, ἢ ὅτι ἀδύνατον ἢ ὅτι αἰσχρὸν καὶ τὰ ἑξῆς.

Hermogenes, Περὶ εὑρέσεως, 4.12