A person who can be defined as both a 'lunatic' and a 'prodigy', clearly showing both nouns in every day life. A person who is obviously insane, yet still shows remarkable smarts/skills in a profound field. Someone who's really smart but fucking nuts.
'Dude, my little brother gets all A's and plays piano, yet when he gets home from school, he tortures our dog and never listens to a word we say! He's a freaking lunagy!'