My sons are 11 and 8. They can both be prone to silliness, that is expected, they are children. But ds2 is a real windup merchant.
We always have issues in the car. If he is at the front, he annoys me by either touching me, playing with the controls, the radio, grabbing my phone (with gps running). If he is in the back with his brother he will start fighting with him. If his brother is in the front and he is alone in the back, he will throw things forward. Like a toy, or bits of paper.
If we are at the bank, or like today at the embassy to sort passports, he forces me to keep his focus on HIM rather than let me do what I have to do, so I get side tracked and stressed.
I hardly ever bring them with me to do stuff for this reason but sometimes it cant be annoyed.
I honestly dont know what to do. Sanctions dont work. He does not care. He is all smiles and "I love you mum" whatever I do.
After all this stress, they did NOT get the treat of cake in the top floor of Peter Jones in Sloane Square with views over London, we headed straight back to "our village", where we had another errand, to open ds2s childrens account with card.
The whole trip had been such a palavar that when I heard lots of faffing and shoving behind me, I turned to look, and stumbled in a lose paving stone and have sprained my ankle.

We did not go to the bank, we hobbled back to the car and I drove home.
And I did not bother making home made nachos pizza as I had promised. I cant walk. 