(n): A person who claims another's work, especially jokes, as their own. Usage popularized on The Simpsons when visiting italy and seeing a picture of Family Guy's Peter Griffin in an italian book of criminals.
Adam: Wow, that Andrew sure is funny.
Mike: Ya, but I like his jokes the first time I hear them... when Rod invents them.
Adam: What? They're not Andrew's own works?
Mike: Nope. He's a total plagiarisimo.