Involves two persons. One individual with food or some chewable foreign object in his or her mouth positions said on their upper or lower teeth. The other person positions their mouth in such a way as to chomp or "gnash" the food or foreign object. During the gnashing, saliva is usually produced and maybe used as a lubricant for various sexual activities.
Shaun and I had sex after gnashing a piece of gum he found in a public washroom.
by STUN January 07, 2006