Take off

This is a famous Korean horror animation short called “Take Off” (also known as “Beauty is Only Skin Deep” or “탈피” in Korean), created around 2008–2009 by a student or independent animator. It’s a very short (about 1-minute) horror/comedy piece that went viral in the late 2000s and early 2010s.
What happens in the video (step-by-step):

A cute anime-style girl with blue hair is getting ready in front of the mirror, putting on makeup and admiring herself. She looks perfectly normal and pretty.
She starts removing her makeup… but instead of just wiping off comes the makeup, she literally peels off her entire face like a mask.
Underneath is a grotesque, hollow-eyed, decayed skull-like face.
She casually takes out fake eyeballs from her empty sockets and places them on the table.
Then she peels off her lips (which are also fake), revealing jagged monster teeth.
She removes her entire human skin like a suit, revealing a brain on top and rotting flesh underneath.
Finally, her “hair” turns out to be a giant purple centipede-like monster that detaches and scurries away in panic.
The girl (now just a walking corpse with a brain and monster teeth) calmly continues putting on her makeup in the mirror as if nothing happened.

The punchline/text at the end says:
“BEAUTY IS ONLY SKIN DEEP”
It’s a darkly humorous twist on the saying — literally showing that beauty is only the thin layer of fake human skin she wears. Underneath, she’s a monster, but she still wants to look pretty for the outside world.
The animation became a meme/classic internet horror short because of how cute it starts and how suddenly and extremely disturbing it gets. Very effective shock humor.