From the episode
Oil On Candace, Doofenshmirtz tells Perry the Platypus in true broadway fashion how he must impress his professor from his evil school days...
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Doofenshmirtz: Back in class, Evil 101...
I always had so much fun...
Though the one who advised me...
Openly despised me...
Still I always tried to be number one
Well I wanted a mentor to share my world view
But I got a tormentor, I was hated, it's true
Now I have one more chance, and it could mean my advancement
So there's only one thing I must do:
I must impress my professor
Singers: (He's got to be good)
Doofenshmirtz: I must impress my professor
Singers: (He's misunderstood)
Singers: He needs validation for his evil creation
Doofenshmirtz: (Oooh-oooh)
Doofenshmirtz: Like any good evil scientist would
Doofenshmirtz: I must impress my professor to be a success
Singers: He must impress his professor to be a success
Doofenshmirtz: Or I will still be a flunky, a diploma-less monkey
Singers: Or he will still be a flunky, a diploma-less monkey
All: In the eyes of this person
Who's opinion may worsen
Doofenshmirtz: If my evil invention's not great
Doofenshmirtz: I must impress my professor!
Singers: (Impress his professor)
Doofenshmirtz: I must impress my professor!
Singers: (Impress his professor)
Doofenshmirtz: I must impress my professor
All: Before it's too late!