Conceited as a midshipman (6)
I believe the answer is:
snotty
This clue is a double definition.
'conceited' is the first definition.
(I've seen this before)
'a midshipman' is the second definition.
(I've seen this before)
'as' acts as a link.
(Other definitions for snotty that I've seen before include "Snobbish" , "Showing contempt, too big for one's breeches" , "Midshipman" , "superior" , "Conceited - foul with nasal discharge" .)