Most people show up to BAM — the Brooklyn Academy of Music — either way overdressed or visibly uncomfortable. You see someone in a full sequin gown next to someone in ripped jeans and a hoodie. Neither looks right. Neither looks wrong. But both of them missed the point: BAM is not a Broadway theater. It’s not a dive bar. It’s a specific, weird, wonderful middle ground. And the outfit rules are different here. I’ve been going to BAM for about eight years now — dance performances, film screenings, opera, the Next Wave Festival. I’ve made every mistake. I’ve worn…