If there is anything I have learned over the years, there is no guarantee that a person who falls into a minority (of any kind) will be accepting of other minorities.

Many gay men and lesbians look down on bisexuals and transfolk (as do heterosexuals).  Many gay/lesbian leatherfolk look down on non-leather BDSM, or refuse to accept a het or bi person as a leatherman/leatherwoman.  A lot of BDSM folks look down on switches, or claim they don't exist (just like many claim that bisexuals don't exist).  Many members of ethnic minorities look down on other ethnic minorities.  Etc. etc.

The important thing is to call these idiots on their bullshit.

That's the beauty of being bisexual.  I like penises AND vaginas, and everybody has an ass, mouth, and hands (as the poll says).

Tell him to suck it up and use lube.  It doesn't change the sensation THAT much.

By the time you feel pain, the damage may have already been done.