Bboy=Break Boy, Bronx Boy, and something else that I forget. They call it breakin because the bboys and bgirls usually jump into the cypher at the break of a song.
Break Boy, comes from DJ Kool Herc naming "Breakdancers" after a street termanology. (break basically means to do thingsout of the ordinary or above normal)
The word break in breaker boy is refering to a part of a song where it gets hype what they use to call the break in the song the person whould start dance so every time the break in the song came on they would dance
It was originally made to be "beat boy" because no one had associated that type of gymnastic dance to the word break yet. Now it can be associated directly with breakdancing.
BBoy is short for bitch boy. That one bitch faggot which noone likes. Bitch boys are also basically cucks, if you see a bboy you fucking flame them and beat them up.