off-the-wall

Wildly unconventional; bizarre; absurd.

What kind of a harebrained, off-the-wall idea is that?

She is a very off-the-wall character.

Of a person's behaviour: greatly inappropriate.

All of their friends were amazed that they were familiar with a war hero. Some began to understand Chips' moods and drinking. His "off the wall" behaviour at times. And unknowingly they were "forgiving" him.