What is Loony ?
Loony is (adj) silly or crazy (informal.) He had this loony plan to cycle round Africa. That’s the looniest idea I’ve heard yet! (NOTE: loonier – looniest) (noun) a person who is regarded as silly or crazy (insult.) Whoever invented bungee-jumping was a bit of a loony. (NOTE: The plural is loonies.)
source: Easier English, Student Dictionary Upper Intermediate Level