loony
n. countable B2 Upper Intermediate US //ˈɫuni// UK //lˈuːni// loony
n. a person who is considered to be mentally unbalanced or acting in a very strange way. It is a very informal and slightly rude word for someone who is acting crazy.
n. a person perceived as mentally unstable or behaving in an irrational, eccentric, or foolish manner. Highly informal and often considered vulgar or derogatory depending on the context.
He is such a loony for thinking he can fly.
The crowd laughed at the loony who was wearing a full suit of armor in the middle of the street.
While some critics dismissed the director as a loony eccentric, his latest film has actually been hailed as a masterpiece of modern cinema.
Shortened from lunatic, and likely also from loon ("rascal", and also the bird) + -y.