Opera houses gave up decades ago
The idea that you need formal dress for the opera is a persistent myth that costs houses money and keeps audiences out. At Covent Garden, the Met and almost every house in Europe you will find black tie and jeans in the same row, and nobody comments on either.
The two real exceptions
Premieres and season openings are genuine social occasions where the audience dresses and enjoys doing it. The 7 December opening at La Scala is a national television event with protesters outside and evening dress inside. The other exception is the private ball, at the Venice carnival and elsewhere, where costume is a condition of entry and hire shops exist for exactly that reason.
The rule that runs backwards
At the serious techno clubs, expensive and branded clothing works against you. Berghain is the famous case: black, plain and unbothered gets further than anything designed to be noticed, and arriving in a large, loud group is the single most reliable way to be refused.
What actually matters
Shoes, for anywhere you will stand or walk on stone. A layer for outdoor venues, because the Hollywood Bowl and the Waldbühne both lose ten degrees after sunset and every summer audience underestimates it. And something with a pocket, because cloakrooms have queues at both ends of the evening.
Cities differ
Milan dresses better than anywhere in this guide and enjoys being looked at. Berlin does the opposite with equal conviction. Vienna keeps a formal audience in the seats and a completely informal one at the standing rail, in the same performance, and neither minds the other.
