It is illegal to wear a hat in a theater if it blocks the view of the person sitting behind you.

The Law

In the late 19th and early 20th centuries, women's fashion heavily featured massive, ornately decorated hats adorned with feathers and ribbons. Theatergoers grew furious when they paid for a show only to stare at the back of someone's elaborate headpiece. City councils eventually passed ordinances requiring patrons to check their oversized hats before entering the auditorium.