You, young man, I want to start with you. When you go about wearing tight hose on your legs, with laces all around it, with your leg exposed, and your hose undone and broken, and your little doublet riding up to your belly, with this behavior you clearly show what you are. In the same way when you return home, you take your doublet off in front of sisters and sisters-in-law and your female relatives, and they see all sorts of crudeness, and with this sometimes one goes on to other things...You, young man, don't you care about anything? Know that God does not like it when you wear hose, or the way you wear it, with the leg open or cut up, and with your little doublet so short...
He goes on to criticize the giornea, an overgarment that's open at the sides and held in place by a belt, creating tight folds:
Have you considered how the giornea is made? It's made like a small blanket for horses, with fringes at its sides and at its feet, and so you wear clothes just like an animal. This means that on the outside you are a dressed-up animal. Judging from the fact that you dress like an animal on the outside, one can assume that you must be an animal on the inside as well.
In 1497, Friar Domenico da Pescia, who was Savanarola's appointee to oversee the reformation of Florentine youths, admonished them to "keep your hair a proper length," because many young men were growing it past the appropriate mid-ear length.
It's also fun to see paintings where fifteen-century teenagers are behaving like, well, teenagers. See the cluster of frisky young adults in the bottom right corner of this painting, The Allegory of April, by Francesco del Cossa in the Palazzo Schifanoia:
The more things change, the more they stay the same.
From: Clothes and Teenagers: What Young Men Wore in Fifteen-Century Florence, by Ludovca Sebregondi (in The Premodern Teenager, edited by Konrad Eisenbichler)