"I was just..."

I know it's just a stage because I remember it well from when Marcel was this age, but it still drives me quite mad. It is when your child is doing something annoying, say humming at the table when you are trying to eat, tapping their fork on their plate incessantly or dancing backwards and forwards across the living room between you and the person you are trying to have a conversation with. You turn to him and gently say 'Léon, gonna not do that' and he replies instantly in a very sweet voice 'I was just humming/tapping/dancing' etc. Arg! 'I know what you were doing! That's why I asked you to stop doing it! I don't need you to explain what you are doing to me because I can see/hear what you are doing! That is why it is driving me mad!' And when you explain this, he looks at you wide-eyed, with a confused expression and launches once again into a more intricate version of 'I was just...'  

Maybe I could have an 'I was just...' box, the way some people have swear boxes. Every time he says 'I was just...', he could put in 50p and by Saturday night every week, we could all go out for a meal in a restaurant!