Related Clues:

• Unrealistic one
• Eccentric one
• Certifiable
• Odd fellow
• Non compos mentis
• Considerably less than all there
• Gaga
• Far-fetched, as an idea
• Round the bend
• Bananas or nuts
• A few bricks shy of a load
• Mad as a hatter
• Very foolish
• Crazy or impractical person
• Fruitcake, screwball