-Man, she looks fine!
-Can't you tell? That's a horrible pixelated shot of an underdeveloped highschool freshman in their underwear trying their best to make a seductive face, dude.
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.
unimpressed, unmoved, disappointed by lack of cerebral prowess or performance, failure to meet expectations, failure to provide evidence to support arguments
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."