Lad likely to go wrong? Romeo, Romeo! (4-6)
I believe the answer is:
lady-killer
'romeo' is the definition.
(I've seen this before)
'lad likely to go wrong? romeo' is the wordplay.
'to go wrong?' is an anagram indicator (I've seen 'going wrong' mean this).
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'likely' with letters rearranged gives 'ykille'.
'lad'+'ykille'+'r'='LADY-KILLER'
(Other definitions for lady-killer that I've seen before include "Man irresistibly attractive to women" , "Irresistible philanderer" , "Man who thinks he's good with the girls" .)