the inherited instinct to nod your head at people; if you know them or not, and it takes no thought process for initiation or to respond. mostly like predominate in caucasian males, but stretches every ethnic back round in the united states. IRN
for short. it's a non verbal way to say i see you there, or to recognize what is going on in a particular environment.
bicyclist and driver give a impulsive recognition nod at one another as to agree not to collide with one another.
male friend see's another male friend having a conversation with a female and gives the impulsive recognition nod as to non verbally communicate a variety of things such as; leave me alone, find your own ride home tonight, yes am trying to have sex with this individual, good luck etc.
you catch a person looking at you and that individual gives a impulsive recognition nod, and nod back but don't know why. this prevents any unnecessary altercation due to the IRN