Cretin: Although this word comes from cretinism, mental illness which was very common in some places where the land was very poor in iodine, possibly originated is back in the island of Crete, where Paul the Apostle mentions in one of his letter writing to Tito his partner Titus 1:12 was one of their own prophets who said: "The Cretans are always liars, evil beasts, lazy gluttons.".It is clear that cretin is synonymous with stupid, silly, lerdo etc.
I understand that geeky phrase comes from the city of Crete, because apparently they had the labyrinth of Crete and had dominated to Athens and sacrificed you human the Minotaur fed on the offerings and the Cretans also them lola they ate. Bone that a cretinada was what they were doing, there comes the word asshole