So the term FB was originally a slur used against trans women and transfems，and is rooted in transmisogyny and the porn industry，which is extremely exploitative and shit when it comes to trans people in general．
Here's an explanation from my friend，Elias．It better explains this than I do．
＂not only is the term heavily rooted in tfem transphobia but is also rooted to the corn industry + nsfw content. that industry is extremely exploitative and transphobic about trans people and encourages fetishization of trans people＂