Drunken prince guzzling first of oysters like a pig (7)
I believe the answer is:
porcine
'like a pig' is the definition.
'drunken prince guzzling first of oysters' is the wordplay.
'drunken' indicates an anagram.
'guzzling' means one lot of letters goes inside another (I've seen this in other clues).
'first of oysters' becomes 'o' (1st letter of 'oysters').
'prince' is an anagram of 'prcine'.
'prcine' placed around 'o' is 'PORCINE'.
(Other definitions for porcine that I've seen before include "Swinish" , "Of or like a pig" , "Filthy" , "Of pigs" , "Piggish" .)