I have very, very little time for Tumblrsexualities, but I think there is a useful, if largely academic, distinction to be made between bisexuality and pansexuality.
I think I am bisexual rather than pansexual because the nature of my attraction to girls is different from what it is to guys. I have not the slightest whit of desire to enter into an emotionally involved relationship with another guy and I am highly particular about what sort of guys I like. That looks fetishistic to me. And I have often thought that it might be possible for an expressed sexuality to be the result of either a true orientation or a fetishised attraction.
Oh, and I think it's stupid and facile, not to mention a bit insulting to transsexuals themselves, to repurpose the word "pansexual" to describe those who are attracted to transsexuals.