skin·ny
/ˈskinē/
Adjective
(of a person or part of their body) Unattractively thin.
Noun
Confidential information.
Synonyms
lean - thin - gaunt - scraggy - scrawny - meager - meagre
Skinny means Unattractivley thin, so why do you want to be that?
So, skinny is not the meaning of Pretty or Beautiful.
Skinny is ugly.