Arrogant boy out to mess - but not with me! (5)
I believe the answer is:
bossy
'arrogant' is the definition.
(thesaurus)
'boy out to mess but not with me' is the wordplay.
'boy' becomes 'b' (abbreviation used in schools).
'out' is an insertion indicator.
'to' becomes 'oy' (I can't explain this - if you can you should believe this answer much more).
'but not with' is a deletion indicator.
'mess' with 'me' taken out is 'ss'.
'oy' going around 'ss' is 'ossy'.
'b'+'ossy'='BOSSY'
Can you help me to learn more?
(Other definitions for bossy that I've seen before include "Disagreeably domineering" , "Domineering (colloq.)" , "Fond of giving people orders" , "As overbearing type" , "Autocratic" .)