Y'know how "edgy" teenagers wear leather cuffs or whatever weird crap so that they look "edgy" and "cool" to their friends but to all other members of society they just look like tools? I think that's the FA movement: wearing a crop top so they can show their three friends how they've bought into the meta and are "fierce" and "proud" but to everyone other than those three friends, they're a joke. Unsurprisingly I assume that there's a bit of overlap between the teenagers that dress like anime characters on the daily and the people who become "fierce and proud" members of the FA movement.