Basically every scene where Doofenshmirtz realizes it's Perry (who's in a disguise at the time, then he takes it off and wears his fedora) who he's seeing/talking to:
- Whether it be him playing a musical instrument ("Attack Of The 50-Foot Sister") ...
Doofenshmirtz's Jingle Singers: Doofenshmirtz Evil Incorporate—
Heinz Doofenshmirtz: Oh, what now?
(Perry staggers in, playing a banjo)
Heinz Doofenshmirtz: A banjo-playing platypus?
(Perry puts on his secret agent fedora)
Heinz Doofenshmirtz: PERRY THE BANJO-PLAYING PLATYPUS?!
- ...Or him acting out a job which he's bad at ("The Lemonade Stand") ...
Doofenshmirtz: What kind of a plumber are you?
(Perry takes off hat)
Doofenshmirtz: A platypus plumber?
(Perry puts on fedora)
Doofenshmirtz: Perry the Platypus Plumber?
(Perry takes off his plumber belt)
Doofenshmirtz: PERRY THE PLATYPUS??!!
- ...Or him being in another person's body ("Does This Duckbill Make Me Look Fat?") ...
(Perry, in Candace's body, busts into Doofenshmirtz's building)
Doofenshmirtz: A teenage girl?
(Perry puts on his fedora)
Doofenshmirtz: PERRY THE TEENAGE GIRL?!
(He presses a remote, a cage falls on Perry)
Doofenshmirtz: Sorry about the tight fit, but you know, if I had known you were going to disguise yourself as a teenage girl, I would have set a bigger trap.
- ...Or him disguising as a thing Doofenshmirtz is supposed to be stealing (Lawn Gnome Beach Party Of Terror) ...
Doofenshmirtz: (collecting his stolen lawn gnomes, gets Perry disguised as a lawn gnome next) Oh, here's a funny looking one. (Perry punches Doofenshmirtz)
Doofenschmirtz: What the—?
(Perry takes off his disguise)
Doofenshmirtz: A platypus?
(Perry puts on his fedora)
Doofenshmirtz: PERRY THE PLATYPUS?!
- ...Or him disguising as someone Doofenshmirtz hired ("Flop Starz") ...
Dr. Doofenshmirtz: (when Perry comes in wearing Groucho Marx glasses) Oh, are you my new temp? Well, let me just get you up to speed; I know it's a bit of a piece of dirty mess. I'm just putting the finishing touches on my latest maniacal plan. You see, in a few minutes, I will unleash an unprecedented reign of terror upon the entire... (holds up magnifying glass to a map of the world behind him) Tri-State Area, and Perry the Platypus will never be the wiser! (Perry removes glasses) PERRY THE PLATYPUS?! You're a temp? Are times that hard?
- ...Or Doofenshmirtz accidentally buying him and planning to use him on his schemes (Got Game?) ...
(After Perry knocks Doofenshmirtz down and takes his Misbehavinator)
Doofenshmirtz: Hey! What was that all about?
(Perry takes off his dog disguise and puts on his fedora)
Doofenshmirtz: Perry the Platypus?!? Uh, ha ha, I...I'm very embarrassed about all that 'coochie-coochie-coo' stuff...
- ...Or Doofenshmirtz not being able to immediately recognize Perry ("Tree To Get Ready") ...
Pretty good don't you think, Perry the Platypus? (spits out drink)
PERRY THE PLATYPUS?! (screaming to pigeons)
Get him!!! Stop him!!! He's headed for that clearly-marked exit!!!
- ...Or Doofenshmirtz realizing that he brought Perry along when he tried to escape from him ("One Good Scare Ought To Do It") ...
Okay, let's make sure I didn't forget anything in my haste. Let's see, I've got my old basketball, the lamp, the Christmas lights, Perry the Platypus, the Disintivaporator, my golf clubs... PERRY THE PLATYPUS!? [Beat
] THE DISINTIVAPORATOR!? [Beat
] MY GOLF CLUBS
!? I don't even play golf!
- ...Or him trying to impersonate someone Doofenshmirtz idolized ("A Hard Day's Knight").
Perry: (mouthing a CD recording) Upon an evil winter's heart, the heavy hand of regret infrequently alights. The malevolent part is one charm without the cumbersome shackles are sentimental intro (the CD begins skipping) spect spect spect spect spect spect spect spect spect spect (Perry whacks the CD player with the book)
Dr. Doofenshmirtz: Hmm, that's funny. I don't remember you saying "spect" so many times. (Perry explodes out of his disguise) Dr. Wexler, you're a platypus. (Perry puts on his hat) PERRY THE PLATYPUS!?
- ...Or Doofenshmirtz happening to bump into him and recognizing a resemblance from his disguise ("Vanessessary Roughness").
- Actually a subversion; he didn't managed to fully recognize Perry since he didn't take off his disguise and put on his fedora.
Dr. Doofenshmirtz: (crashes into Perry) Hey watch where you're... Say, you look fabulous! But haven't I seen you somewhere before?
- ...Or Doofenshmirtz happening to recognize an item which looks just like him ("Hip Hip Parade") ...
(Doofenshmirtz falls on the Perry balloon of the parade)
Doofenshmirtz: A platypus balloon?
(balloon hits a sign and the fedora from the sign falls on the balloon's head)
Doofenshmirtz: A PERRY THE PLATYPUS BALLOON?!
- Go to the movie page for perhaps the best examples ever of Doof not recognizing Perry.
- ("Mommy, Can You Hear Me?")
(Perry is trapped. He shakes off his hat and enters pet mode)
Doofenshmirtz: Aw, poor little regular platypus. Did mean old Perry the Platypus put you in this trap?
(He frees Perry who immediately attacks him and puts his hat back on)
Doofenshmirtz: PERRY THE PLATYPUS? I don't know how you got free, or what you did with that other platypus, but it doesn't matter.
- Or for that matter on All Hallow's Eve...
Doofenshmirtz: And what are you supposed to be? A kid in a sheet?
(The "kid in the sheet" takes off the sheet to reveal...)
Doofenshmirtz: A platypus in a sheet?
(He puts on the fedora)
Doofenshmirtz: PERRY THE PLATYPUS IN A SHEET?!?!
- This is also extended to Major Monogram without his moustache in ("Save Summer"), and Monogram has to put his fingers beneath his nose for Doof to recognize him.
- ...Doofenshmirtz will never be the wiser!!