1.) A method of assessing sudden changes in temperature instantaneously by visually (or physically) analyzing the level of hardness(Mohs Scale), angle (preferably in radians), shape, and in odd cases smell, of the nipples.
2.) A sixth sense which detects danger, specifically rape.
n. nipple trajectory
pl. nipple trajector(ies)
1.) My nipple trajectory indicated an oncoming snow storm; I better head inside.
2.) As I walked down the the dark alley, my nipple trajectory activated as the mustached man started to tail me.