This is the song Stewie performs after Brian calls him a douche in the episode 
Ocean's Three and a Half.

     G                    C             D
Then Brian comes in and I change up the tempo
G                    C             D
Brian comes in and I change up the song
G                     C            D
Looking at me like he thinks I'm a douchebag
    G                       C              D
But he's gonna learn pretty fast that he's wrong

Am                      Em
Why are you bringing me down, man?
Am                      Em
Why are you bringing me down?
Em
Don't bring me down!

(On the last line do a hard strum with each word)

Enjoy.