noun
fashion leader; fashionista
A playful term for someone who is notably stylish or a trendsetter in a group, often used among young people.
彼女はクラスのおしゃれ番長だ。
She is the fashion leader of the class.
おしゃれ番長と呼ばれるほどセンスがいい。
He has such good taste that he's called a fashionista.
おしゃれ is a general adjective/noun for 'stylish' or 'fashionable', while おしゃれ番長 specifically refers to a person who is a fashion leader.
ファッションリーダー is a more formal, loanword equivalent, whereas おしゃれ番長 has a playful, slightly old-fashioned schoolyard feel.
Compound of おしゃれ (fashionable, stylish) and 番長 (boss, leader of a gang). The term likely originated as school slang, likening a fashion-conscious person to a 'gang leader' of style.