Big-Lipped Alligator Moment: The episode opens with Pinkie suiting up in a leotard, leg warmers and headband and doing a Flashdance routine for the Cake twins. Aside from having Pinkie in it, it has absolutely nothing to do with the rest of the episode. YMMV, as it could be seen as an example of the lengths to which she will go to make friends smile, which is the point of the whole episode.
Broken Base: The whole episode (yes, another one). Putting aside Pinkie's song, you either love this episode because it delves into surprisingly mature (by this show's standards) territory and its hilarious Looney Tunes-esque gags, or you hate it because it turns Pinkie into an unlikable MareFilly and having an ultra-contrived happy ending.
Designated Villain: We're supposed to side against Cranky throughout the episode because he's grouchy and repeatedly tells Pinkie Pie to buzz off. Pinkie annoys him to no end simply because he's new to Ponyville and wants to fulfill her new friend quota. Her being too Innocently Insensitive and constantly barging in on his life (which includes breaking into his house and destroying his possessions) makes Cranky a sympathetic character who rightly calls her out on such intrusiveness.
The scene where Pinkie sticks her eyeball through the lock... GAAAAH!
Also, the dough-Pinkie, with black holes where her eyes should be. Then Pinkie eats Dough!Pinkie.
Padding: As awesome a song as "Smile Smile Smile" is, did it really need three and a half minutes of screentime just to re-iterate that Pinkie Pie is friendly and nice?
Paranoia Fuel: Pinkie Pie's mission to get to know everypony in Ponyville. This takes a drastic turn when she obsesses over Cranky.
Ship Tease: Rarity's name for the wig she gives Pinkie to give to Cranky is called the Dreamboat Special. That said, put into account that it looks almost exactly like the hairdo worn by Steven Magnet...