It stands for WhamBam as in the WhamBam improv jam held through Second City Hollywood weekly. It is used in the chat section of as a form of acknowledging humor or skill.
Weekend bitch
Typically used to describe a person, one hooks up with on weekends.
A difference in status is implied when using this term.
Rub my feet, wb, it’s weekend, bitch.
it means what about / what 'bout
John : Lets go to six flags at 11am
Sarah : Wb 12
John : Bitch wtf is wb
Sarah : Nigga@!#!# "what about"