Former pupil with view that's disgusting (7)
I believe the answer is:
obscene
'disgusting' is the definition.
(obscene can mean disgusting or indecent)
'former pupil with view' is the wordplay.
'former pupil' becomes 'OB' (abbreviation for 'Old Boy').
'with' is a charade indicator (letters next to each other).
'view' becomes 'scene' (synonyms).
'ob'+'scene'='OBSCENE'
'that's' acts as a link.
(Other definitions for obscene that I've seen before include "Shocking" , "coarse!" , "off colour?" , "Sexually offensive" , "unsuitable for children?" .)