A Grunter, is someone who is very ugly and usually has a huge bottom jaw. When you look at a grunter its almost impossible to not picture them acting like an ape throwing the poo everywhere. There are different levels of grunting, a high level grunter would deemed, "He Grunts On A University Level" whereas most just grunt on a 6th grade level.
Dylan: WHOA Shlab...Check out that Grunt Lord!
Sean: Holy Shit! that Grunter looks like he's the type of guy to eat a load of shit every morning!