I'm in a closed poly triad (MFF) so my girlfriends who are bi finally stopped getting the comments you're talking about as they both have a M and F partner. It's sad that it took that for people to stop making those comments. It sucks that you have to have one of each partner for people to consider your bi-ness "real".
Not exactly related but I also get the "outsider" feeling when it comes to pride as I've always considered myself straight (I never would pursue a guy but if a hot guy pursued me I would probably enjoy it) and now I've gotten comments calling me "double straight" as I have two female partners. Poly isn't exactly in the LGBTQ so I definitely get the "ally" treatment.
Sameeeee...