A and B the C.O.D. - You did so much more than you had to that you might as well

You did so much more than you had to that you might as well have been doing it for fun and to piss people off.

I answered the phone, then started a debate with the caller about the meaning of life.

I cleaned my room, then threw my socks at my brother.

I finished the test, then drew a mustache on the teacher's face.