Noun. NRB ( No Reason Boner)
This is what all male humans experience spontaneously, occuring from the early ages of adolesence to even in some rare cases senilty. NRB can attack men unkowningly, silently, and suddenly causing possible embarassing situations or even discomfort.
Zach was wearing basketball shorts walking to third period when he suddenly got an NRB and caused laughter and jeering from students around him.