Loony (adjective)

1. Crazy, eccentric, or insane.
2. Silly or ridiculous.

Origin:

Early 20th century: from loon, with reference to the bird's wild or crazy call.

Examples:

1. He was called a loony for his eccentric behavior.
2. The loony idea of traveling to the moon was considered impossible.
3. Her loony laughter filled the room.
4. The loony old man was always talking to himself.
5. The loony scheme was never going to work.