(loonies, loonier, looniest)
1.
If you describe someone’s behaviour or ideas as ~, you mean that they seem mad, strange, or eccentric. Some people consider this use offensive. (INFORMAL)
What’s she up to? She’s as ~ as her brother!
ADJ disapproval
2.
If you refer to someone as a ~, you mean that they behave in a way that seems mad, strange, or eccentric. Some people consider this use offensive. (INFORMAL)
At first they all thought I was a ~.
N-COUNT disapproval