Annoyed, if following sea around (6)
I believe the answer is:
miffed
'annoyed' is the definition.
(I know that annoyed can be written as miffed)
'if following sea around' is the wordplay.
'following' becomes 'f.' (used when citing page numbers etc).
'sea' becomes 'med' (short for Mediterranean).
'around' is an insertion indicator.
'if'+'f'='iff'
'iff' inserted within 'med' is 'MIFFED'.
(Other definitions for miffed that I've seen before include "Disgruntled" , "Annoyed, hacked off" , "Aggrieved" , "Informally offended, put out" .)