UnderFell is an Alternate Universe created by fans. The main idea of it is everyone is their cruel counterparts, and apparently only wear orange, black, and red.
To undersee something is to get out of that fugue state-of-mind and simply see something for what it is instead of, the inferior, understanding what's going on.
Dude 1: "... And that's how it all happened."
Dude 2: "Dude... DUDE!"
Dude 1: "Yeah?"
Dude 2: "Not only do I understand... I UNDERSEE IT!"
Dude 1: "Dude, that's wicked. Lets smoke a J."
John: I forgot to feed to my dog and it was taken away because it was "underfed", what does that mean?
Sal: You didn't give it enough derf idiot, take better care of your pets.
An adult who has not had enough sex, commensurate with his/her age.
Undersexed individuals find themselves in a vicious circle. Because they lack the sexual experience, they are not confident about sex and hence they rarely get any.
Many serial killers were undersexed. Harvard students are undersexed. Hence, Harvard students are serial killers