Sup rum with pastry one disliked after rising (7)
I believe the answer is:
upstart
'one disliked after rising' is the definition.
(unpopular newly successful person)
'sup rum with pastry' is the wordplay.
'rum' indicates an anagram (rum can mean strange or unusual).
'with' means one lot of letters go next to another.
'pastry' becomes 'tart' (type of pastry).
'sup' is an anagram of 'ups'.
'ups'+'tart'='UPSTART'
(Other definitions for upstart that I've seen before include "Arriviste, parvenu" , "Arrogant person new in high position" , "Bumptious parvenu" , "Arrogant Johnny-come-lately" , "pretentious person" .)