In fact, pretty much any reference to an episode that was aired at the time the game was released.
In Rock Bottom, standing near the vending machine at the start will cause a cutscene to start where a bus drives up, idles for a moment, then drives right off, a clever and possible to miss reference to the episode "Rock Bottom".
Five words: Retirement Home Girls Gone Wild.
In the dream world, there was a level intended for Patrick that would've been dessert-themed. However, for reasons that aren't clear, it was cut. The developers, seeing a prime chance to make another reference to the show, just make Patrick's dream a pitch black room with him standing under a spotlight where he just gives you the golden spatula you would've had to work for without any strings attached.