There are certain things in which mediocrity is intolerable: poetry, music, painting, public eloquence.
What torture it is to hear a frigid speech being pompously declaimed, of second-rate verse spoken with all a bad poet’s bombast!
 
[Il y a de certaines choses dont la médiocrité est insupportable: la poésie, la musique, la peinture, le discours public.
Quel supplice que celui d’entendre déclamer pompeusement un froid discours, ou prononcer de médiocres vers avec toute l’emphase d’un mauvais poète!]

Jean de La Bruyère (1645-1696) French essayist, moralist

The Characters [Les Caractères], ch. 1 “Of Works of the Mind [Des Ouvrages de l’Esprit],” § 7 (1.7) (1688) [tr. Stewart (1970)]
    (Source)

(Source (French)). Alternate translations:

Several things are insupportable if they are but indifferent, as Poetry, Music, Painting and Public Speeches.
'Tis the worst punishment in the world to hear a dull Declamation deliver'd with Pomp and Solemnity, and bad Verses rehears'd with the Emphasis of a wretched Poet.
[Bullord ed. (1696)]

Somethings are insupportable if they are but indifferent, as Poetry, Musick, Painting, and Publick Speeches.
What a Punishment is it to hear a cold Declamation deliver'd with Pomp and Solemnity, and indifferent Verses repeated with all the Emphasis of a bad Poet!
[Curll ed. (1713)]

Some things won't bear a Mediocrity, as Poetry, Musick, Painting and Oratory.
What a cruel Torture is it to hear a dull Declamation delivered with Pomp and Solemnity, or bad Verses rehearsed with the Emphasis of a wretched Poet!
[Browne ed. (1752)]

In certain things mediocrity is unbearable, as in poetry, music, painting, and eloquence. How we are tortured when we hear a dull soliloquy delivered in a pompous tone, or indifferent verses read with all the emphasis of a wretched poet!
[tr. Van Laun (1885)]

There are some things that will not bear mediocrity; poetry, music, painting, oratory.
[tr. Lee (1903)]