Decadent principal in school: diminutive, pretty boring bloke? (4-9)
I believe the answer is:
self-indulgent
'decadent' is the definition.
(similar in meaning)
'principal in school diminutive pretty boring bloke?' is the wordplay.
I cannot really see how this works, but
'in' is within the answer.
'school' could be 's' and 's' is located in the answer.
'bloke?' could be 'gent' (both can mean a man) and 'gent' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for self-indulgent that I've seen is " Hedonistic".)