This is my favorite entry in Urban Dictionary, ever. period.
Bisexual:
4. bisexual
The often overlooked B in LGBT. A person capable or romantic and sexual attraction towards a partner of either gender. A person twice as likely to be turned down for a date on Saturday night. Someone who has to prove to the heteros that he is not gay, and prove to the homos that he is not straight. A trait hetero men find extremely attractive in women and seem to find frightening in men.
Some people are bisexual.