A person, usually a male... obviously, that has an intense appreciation of alcoholic beverages (grog). They are not necessarily an alcoholic but just really enjoys drinking grog.
Mate, Johno is a full on grogboy.
He's always got a drink in his hand, he's such a grogboy.
Brian's got a fully stocked bar, he's a legendary grogboy.
He's partying every night like a hardcore grogboy.
Jack Sparrow is a poster-boy for grogboys.