Sailor turning up is unpleasant person (3)
I believe the answer is:
rat
'unpleasant person' is the definition.
(I know that rat is a type of unpleasant person)
'sailor turning up' is the wordplay.
'sailor' becomes 'tar' (slang term for a sailor).
'turning up' is a reversal indicator.
'tar' in reverse letter order is 'RAT'.
'is' acts as a link.
(Other definitions for rat that I've seen before include "Despicable person" , "Rodent pest" , "Treacherous person" , "person doing shopping" , "Tell-tale" .)