Suetonius, in his Vita Horati, reports that the emperor Augustus jokingly referred to Horace as a purissimus penis:
Praeterea saepe eum inter alios iocos purissimum penem et homuncionem lepidissimum appellat, unaque et altera liberalitate locupletavit.
What is this intended to mean? Purus can mean "pure, clean", and also "chaste"; but a meaning "most chaste penis", if that's what's intended, must be ironic, since a little later Suetonius reports that Horace was so lustful that he had a room lined with mirrors in which to watch himself disporting with prostitutes. Is that the joke -- an ironic reference to Horace's lasciviousness?
The Loeb translation gives "a most immaculate libertine", but I'm not sure (a) what that means at all, and (b) whether it represents Suetonius's meaning.