knock something on the head [British]
to show that a story or an idea is not true or correct
It's time to knock on the head the idea that we are not fully human, not fully alive, unless we have that special somebody in our lives.
to decide to stop an activity , or not to start it
I remember us in the early days saying: `When we stop enjoying ourselves, we'll knock it on the head.'
Easy Learning Idioms Dictionary. Copyright © HarperCollins Publishers