They were lying. It means random boner.
“When I was at my family dinner i got an rb”
“Was your aunt Becky there?”
“Yeah.”
“Then it wasn’t random.”
rb stands for rant buddy which technically means you rant to them about something, or they rant to you, or you two rant to each other about how complicated your lives are.
man I could really use a rb right now I can’t deal with my problems anymore.
An abbreviation of the Trinidadian expression 'rock back'. Meaning relaxing or chilling.
yeah man, I just here rb, waiting on somebody.