Abed apologizes to Annie for missing her birthday, Halloween, Christmas, and other major holidays. This is a reference to the lack of holiday-themed episodes in Season Five which was possibly done in order to avoid another Season Four situation. That year NBC rescheduled the debut of the show to February from its announced November date. All of the holiday-themed episodes were aired long after that particular festivity had been celebrated.
Throughout much of the episode, Abed is wearing a t-shirt with the logo for The Dead Alewives. The Dead Alewives were an improvisational comedy group formed in the 1980s in Milwaukee. Series creator, Dan Harmon, and show director, Rob Schrab, were among the founding members.
Dean Pelton's name is revealed to be Craig Isadore Pelton.
127 in binary is indeed a palindrome but that's only because it is 1111111.
The toy rocket launcher the Dean finds on the desk and proceeds to choke on references a 1979 Kenner promotion in which fans could mail in to receive a Boba Fett action figure with rocket launching backpack. The promotion was cancelled before any toys shipped over concerns about the choking hazard.