Phil Ken Sebben: So, I got this tremendous opportunity! My own law firm! Might put my name in the title! Get a big S-shaped desk! Great for interviews! A spin-off, if you will!
Harvey: So... you're leaving us?
Phil Ken Sebben: I wouldn't say that. I'll just be extremely busy on the new show, err, firm.
(Stephen Colbert himself can be seen in the elevator on the ride down, amongst Phil's luggage.)
Alluded to on Colbert's show as well, after pointing out that presidential candidate Mitt Romney had a nervous "ha ha" laugh that sounded similar to Sebben's. He even held up a copy of the DVD, and did the laugh live.
Ascended Fanon: A major joke of the series. The majority of Birdman's cases are based around popular fan theories (Doctor Quest and Race Bannon are actually a gay couple, the Scoobie gang are stoners,Top Cat is really a pimp, etc.) and headscratchers (why can't you see Apache Chief's or Grape Ape's genitals, despite their respective sizes?, why is Secret Squirrel apparently naked under his trench coat?, etc.) related to old Hanna Barbera cartoons.
Billing Displacement: A bit of an odd example: in the parody opening of "The Dabba Don" Barney gets second billing despite only being in two scenes. Given how the ending reveals he's the real mafia boss, it makes a bit more sense. Conversely, despite being the title character and being co-protagonist with Fred, Harvey gets fifth billing. Phil (who only has one scene) and Peanut (who is Harvey's assistant) get higher billing than he does.
Schedule Slip: One of the main downfalls of the series. While the first season aired on schedule, the remaining episodes aired all over the place, with one or two airing then a gap of nearly a year before the next batch aired. Potentially mocked in "Turner Classic Birdman":
Robert Osbourne: You may have heard of the animated show Harvey Birdman: Attorney at Law. In fact, if you're persistent, you can sometimes still catch it late at night on cable.