There are two jokes going on here. One is about the funny-sounding, fake Scandinavian words. The other is sexual innuendo. "Blow my own verturgen-furgen" is a play on the English saying "blow my (your) own horn." "Blow your own horn" means to brag about oneself. Blow is to force air out of your mouth. A horn is a kind of musical instrument that you play by blowing. But "blow" also has the sexual meaning of to give oral sex. So, when Sophia says "I can't even reach mine," she is suggesting that verturgen-furgen actually refers to genitals, and that she cannot even reach that part of her body. "Playing with a full set of balls" here means being a little bit crazy or not being very intelligent. There are many English sayings with a similar meaning: Not playing with a full deck of cards. One beer short of a six-pack. Not the sharpest tool in the shed. Etc.