Is bisexuality normal?

Well I just thought this Like at my school there's lots of like guys (their all normal) who pretend to do gay stuff to each other but their all straight(ish) like theyll all pile on top of each other sit on each others laps and bounce up and down making groaning noises but it's all just for a laugh and stuff but it seems kind of bi to me (I have no prejudice against gays or lesbians)