Suetonius and others record interesting snippets that indicate fashion or cool was a feature of Roman life at various times. “Beware the badly belted boy," Sulla is supposed to have said about Caesar. According to Suetonius, it was noteworthy that Caesar used to wear a loose belt over his tunic, which in his case also had fringed sleeves which reached down to his wrists. This was a bit outrageous apparently.

There was also a case of a trial against a Vestal Virgin accused of breaking her vow, a capital offence, who was instructed by the judge, who found her innocent, to dress in future for holiness and not for fashion.

Follow-up question: What was the opposite of being cool?