Seneca, Letters to Lucullus (1.5):
I approve of the fact and even rejoice that you are diligently striving and, all else neglected, are doing this one thing: to make yourself better every day. I not only urge you, I even beg you to continue. But I do warn you not to do anything which might stand out in your appearance or mode of life, in the manner of those who wish not to succeed but to be seen. Avoid the shagginess, the uncut hair, the neglected beard, the pronounced hostility to money, the elbow placed on the ground, and whatever else ambition may pursue on a decidedly twisted path. The name of philosophy itself, even if it is conducted in a reasonable manner, inspires envy. What then if we should begin to withdraw ourselves from human interaction? Inwardly, all things are dissimilar, but our outward appearance should at least be suited to the masses. Your toga may not shine, but at least don’t let it go filthy; we may not have silver inlaid with gold, but let us not think it a mark of frugality to be without silver and gold altogether. Let us see to it that we pursue a better life than the crowd, but not a contrary one. Otherwise, we will chase away and repel those whom we wish to fix, and we will bring it about that they don’t wish to imitate anything of ours, fearing that they must imitate it all.
Quod pertinaciter studes et omnibus omissis hoc unum agis, ut te meliorem cotidie facias, et probo et gaudeo, nec tantum hortor ut perseveres sed etiam rogo. Illud autem te admoneo, ne eorum more qui non proficere sed conspici cupiunt facias aliqua quae in habitu tuo aut genere vitae notabilia sint; asperum cultum et intonsum caput et neglegentiorem barbam et indictum argento odium et cubile humi positum et quidquid aliud ambitio nempe perversa via sequitur evita. Satis ipsum nomen philosophiae, etiam si modeste tractetur, invidiosum est: quid si nos hominum consuetudini coeperimus excerpere? Intus omnia dissimilia sint, frons populo nostra conveniat. Non splendeat toga, ne sordeat quidem; non habeamus argentum in quod solidi auri caelatura descenderit, sed non putemus frugalitatis indicium auro argentoque caruisse. Id agamus ut meliorem vitam sequamur quam vulgus, non ut contrariam: alioquin quos emendari volumus fugamus a nobis et avertimus; illud quoque efficimus, ut nihil imitari velint nostri, dum timent ne imitanda sint omnia.
Edward Gibbon, The Decline and Fall of the Roman Empire (Chp. XXII):
But with the fopperies, Julian affected to renounce the decencies, of dress; and seemed to value himself for his neglect of the laws of cleanliness. In a satirical performance, which was designed for the public eye, the emperor descants with pleasure, and even with pride, on the length of his nails, and the inky blackness of his hands; protests that, although the greatest part of his body was covered with hair, the use of the razor was confined to his head alone; and celebrates with visible complacency, the shaggy and populous beard, which he fondly cherished after the example of the philosophers of Greece. Had Julian consulted the simple dictates of reason, the first magistrate of the Romans would have scorned the affectation of Diogenes as well as that of Darius.