Look: Of course dressing up as a mass tragedy or culturally-sensitive stereotype is terrible, troubling, and just plain wrong. Dressing up like the Twin Towers or Boston Bombing is worth the public outrage. But this is different. These Bros are dressing up as a pretty significant event in 21st century American history: The moment the United States “Got Him” — the terrorist behind an attack that murdered 2,977 innocent Americans on 9/11 — on May 2, 2011. As I see it, it's not different from dressing as Team America, a costume that's been done countless times over for Halloween since the movie came out in 2004. Clearly that's what's being represented here, as opposed to any perceived cultural insensitivity.
Some things are worth the outrage. I'm not quite sure this is.