Fool of identical twin dismisses nice lad (6)
I believe the answer is:
nitwit
'fool' is the definition.
(both can mean a stupid person)
'identical twin dismisses nice lad' is the wordplay.
I cannot quite see how this works, but
an anagram of 'twin' is 'nitw' which is within the answer.
The remaining letters 'it' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for nitwit that I've seen before include "Plonker" , "Noodle, numskull" , "Fool, idiot" , "'Foolish, silly person (6)'" , "Silly fool" .)