The outlandish quote, "The beast within," is upsetting (6)
I believe the answer is:
exotic
'the outlandish' is the definition.
(I've seen this before)
'quote the beast within is upsetting' is the wordplay.
'quote' becomes 'cite' (synonyms).
'the beast' becomes 'ox'.
'within' means one lot of letters goes inside another.
'is upsetting' says the letters should be written in reverse.
'cite' enclosing 'ox' is 'citoxe'.
'citoxe' written backwards gives 'EXOTIC'.
(Other definitions for exotic that I've seen before include "Having a strange beauty" , "Strikingly strange or unusual" , "Bizarre" , "Glamorous or strange from abroad" , "Foreign, strange or exciting" .)