The word is a fusion of Croat + retard. and is used to denote a person born in Croatia, with exaggerated nationalistic views. Obsessed with defending his countrymen and country, with making sense being an option.
geography teacher: Name the European country with the biggest per-capita income.
croatard: Croatia, obviously!
sports trivia: who is the best football player of the 90's?
croatard: Suker, obviously!