More stupid hoon initially shot in heart (7)
I believe the answer is:
thicker
'more stupid' is the definition.
('thick' can be similar in meaning to 'stupid')
'shot in heart' is the wordplay.
'shot' becomes 'h' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' means one lot of letters goes inside another.
'heart' becomes 'ticker' (synonyms).
'h' inserted into 'ticker' is 'THICKER'.
'hoon initially' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for thicker that I've seen before include "Denser" , "More dense or concentrated" , "'Blood is . . . . . . . than water'" .)