What defines an eelhead more so is its poor vision and inability to see that the person it is escaping from is wearing underwear resulting in brown crayola marks in ones underwear also known as rorschach test marks.
2) The more common nick name for a "Shit Head" as to not offend old ladies and little kids while calling your friend this name.
Eelhead is a more firmer poo that can sometimes have the feeling of what some call a finger in there ass.
"Hey look at that eelhead over there!" or "Your mom is such an eelhead, she won't give it up to me."