When We Didn't Get Along

 is the song from the episode "It's About Time!". The song describes Perry the Platypus's feelings after his nemesis, Dr. Doofenshmirtz, stops fighting him in favor of another secret agent. It is revealed how much Perry's nemesis means to him. Unlike most songs in the series, the singer of this song is not shown on-screen.

Lyrics
Without your schemes my life, it seems, is empty

I spent all my time keeping you from doing wrong

You were my only nemesis

I'd foil your plans, but still I miss

The moments when we didn't get along

So search your heart, please, Doctor D

And I am sure that you will see

That you were always meant to be

My only lifelong enemy

But now you're doing battle with a panda from Seattle

I miss the moments when we didn't get along

Ooh

Extended Lyrics
Without your schemes my life, it seems, is empty

I spent all my time keeping you from doing wrong

You were my only nemesis

I'd foil your plans, but still I miss

The moments when we didn't get along

I fell for you the moment that you pushed me

You captured me and held me for so long

But now you're doing battle with a panda from Seattle

I miss the moments when we didn't get along

So search your heart, please, Doctor D

And I am sure that you will see

That you were always meant to be

My only lifelong enemy

You gave my life heroic cause

Back when my only mission was

The moments when we didn't get along

Ooh

Background Information

 * This song is likely an allusion to the song "When She Loved Me" from Toy Story 2, including similar melody, lyrics, and some similar movements (Such as the shot with Perry being swung in circles).
 * This song, as well as Perry's subplot in "It's About Time!", parodies elements of a romance film. The scene in which Doofenshmirtz and Perry run towards each other on a beach in slow motion makes an obvious reference to romance films, except for the fact that while such scenes in a romance film will end up with passionate moments, Perry punches the doctor in the face when he comes into Perry's reach.
 * This is the first song sung from Perry's POV. The second is I Walk Away.
 * The song has some clips from other episodes.
 * This song has similar instrumental and lyrics with Kenny Rogers' song "Through the Years"