You describe a subject or idea as your hobby-horse if you have strong feelings on it and like talking about it whenever you have the opportunity. Honesty is a favourite hobby-horse for Courau
A child's toy consisting of a (usually wooden or cloth) horse mounted on a stick
A subject or plan upon which one is constantly setting off; a favorite and ever-recurring theme of discourse, thought, or effort; that which occupies one's attention unduly, or to the weariness of others; a ruling passion