N.R.B is an abbreviation for what is known as a "No Reason Boner".A No Reason Boner is when a male randomly "gets hard" for no apparent reason.Also see boner.
No Reason Boner; an erection that pops up outta nowhere.
spoken as: en are bee, or nerb.
"Yeah man, the cop wanted me to get outta the car, but i had an N R B so i just took the heat."
"We broke up (other dude: "why man?"), got a fucking N R B at her grammas funeral."
"If i dont stop gettin nerbs i gonna cut the fucking thing off!!"