Always agree with your boss, especially in front of others.

Let him know that you work to make HIM look good.

You need to value yourself more.  When you do, the office and whatever goes with it carry less significance to you.  You'll feel generous about who gets the credit.  When you give all credit to your boss, the little work you do becomes big in his eyes.  When you hoard all the credit to yourself, your boss will make sure you get more work and questions every credit you claim.  That is him being a boss.

In an office, it is safe not to take the face value of what others say or do, and put more cloth on yourself.