mphobia

Also called multiphobia, mphobia is fear, prejudice, disgust, or discrimination of m-spec (multisexual) individuals.

Note: M-spec stands for multisexual/multiromantic spectrum, which is a spectrum to describe people who are attracted to more than one gender. An example of some (but not all) labels that fall under the category of m-spec are: Pansexual, Bisexual, Omnisexual, and Polysexual.

Note 2: Most urban dictionary definitions of labels stated above are outdated.
Pansexual = Attracted to all genders, regardless of gender.
Bisexual = Attracted to two or more genders.
Omnisexual = Attracted to all genders, except is not "gender-blind" like pansexuals are. They might feel a difference between their attraction to certain genders, or have a preference for a certain gender.
Polysexual = Someone who is attracted to multiple genders, but not all. Contrary to popular belief, this label has nothing to do with polygamy.

Person 1: Hey, I'm Pansexual
Person 2: Why do you have to be attracted to all genders? Can't you just pick one?
Person 1: That's mphobia. Don't say that.