Barking mad British adjective phrase informal
Wild and unpredictable; completely demented, utterly irrational
If you think that plan will work, you're barking mad.
Are you playing tennis this time around? You're mad barking!
There are a few tales connecting 'barking mad' with the Barking suburb of East London. One is that the phrase owes its origin to a medieval asylum that was part of Barking Abbey for the insane. The second story isn't a suggested origin, at the expense of Margaret Thatcher, just a neat 1980s joke.
It was often said by a photographer when he would like small children to look at the camera and smile before he took a photo.
When the photographer said “watch the birdie”, all of us looked at the camera and smiled.