Everybody in the show is superficial (7)
I believe the answer is:
shallow
'is superficial' is the definition.
(similar in meaning)
'everybody in the show' is the wordplay.
'everybody' becomes 'all' (all people).
'in the' indicates putting letters inside.
'all' put into 'show' is 'SHALLOW'.
(Other definitions for shallow that I've seen before include "Without depth" , "Not profound" , "Trivial" , "Superficial" , "incapable of serious thought" .)