Kraftidioten is Norwegian for 'complete moron' or 'total idiot' (literally: power idiot). The term 'kraftidiot' usually applies to people behaving foolishly. It doesn't mean someone is a moron. A person who can't add up numbers would be a regular 'idiot.' A kraftidiot is a mean-spirited person, not stupid. In English, there isn't really a term that applies well.
The Battle of Kosovo (1389) was a battle between the combined army of Serbians and Bosnians against invading Turks of the Ottoman Empire. Both armies suffered heavy casualties, both being basically annihilated. The eventual outcome was the annexation of the Serbian provinces by the Ottomans. The Battle of Kosovo is significant in Serbian history and integral to Serbian national identity.
Greven's car is a Fisker Karma, which is a Finnish electrical, rear-wheeled drive car. Design by Henrik Fisker (Denmark), build by Valmet in Finland.