Biphobia

Biphobia, or bi erasure, is an aversion towards bisexuality, and towards bisexual people as a social group or as individuals. It can take the form of denial that bisexuality is a genuine sexual orientation, or of negative stereotypes about people who are bisexual (such as the beliefs that they are promiscuous, confused, indecisive, or dishonest).

Internalized Biphobia
Internalized biphobia often comes from people who come from an lgbtphobic environment and therefore have a hard time accepting that they are bisexual. They may also have negative feelings towards their sexuality. This happens more often than not and can be seen in the smallest ways, such as someone denying that they are bisexual.

Denial
Some people believe that all bisexuals are actually gay and just in denial. Another similar belief is that bisexuals are actually straight people trying to get into the LGBT+ community.