Why does Prince Charles walk around with his hand in his pocket?

Prince Charles is an organic gardener and works on his garden alongside his staff and groundskeepers. His hands are rough because of it, and he is self-conscious that they are not soft and groomed as one might expect of his stature.

This answer comes from someone who learned this from HRH's staff. Nevertheless, I have seen photos from his youth and he's been doing this for awhile. It appears to be a habit with him.