half the people I've met in my life that claim bisexual status, do so as a means to better their chances with the opposite sex.
Girls that go to a bar together, and use the "idea" of the potential threesome to try and make the chance of getting a man for the night,.. better
Or girls that tell their new boyfriend that they're "bi you know" and so suggest the potential threesome (again) for the sake of making him more interested...