Loony

He's fit for the loony bin.

You know Tom is a loony tune.

Some people might regard belief in ghosts as loony.

If you carry on like this, they'll send you to the loony bin.

Tom said you were a loony tune.

loony scheme

completely loony

They dismissed his loony ideas.

The movie is full of loony characters.

Why, there’s hundreds of lunies of the sort to be met in London.