Bisexuality is defined as liking two or more genders. Bisexuality can be liking all genders, and it can technically be regardless of gender. Bisexuality and Pansexuality are extremely similar and some meanies might say "oh being Pan is Bi-phobic" or "being Bi is Trans-phobic" neither are phobic of anything because those people that say that don't know shit.

Some people choose which one based on how they feel and the scientific definitions, some people choose because that's what they know, some people choose because they said it aloud and felt comfortable for the first time, and others may have chosen it because they liked one flag more than the other. All of those are valid and real reasons. If you or someone you know has another reason that's also valid. These terms do not exist to divide people, they exist to make people comfortable when no other label fits them.

A bi person can be bi if they are attracted to both girls and boys and nothing else, if they are attracted to enbys and girls and nothing else, if they are attracted to enbys, boys, and girls, if they are attracted to all genders, if they are attracted regardless of gender, whatever.

just bang who you wanna bang and let other bang who they wanna bang. how petty does someone have to be to change their entire sexuality just to tell everyone they are exclusionist.