CBRN is a helmet attatchment for Halo: Reach, Grunts however have used it all the time. Most CRBNs look cool, but you just look like you're sucking a dick on some. It stands for: C: Crappy attitude. Chemical. B: Barf Zones. Biological. R: Gygjfrtdcretgvt. Radiation. N: Noob. Nuclear.