When Lucy and Gru are reviewing Paradise Mall shop owners (suspects), the owner of Stuff-A-Bear (a satire of Build-A-Bear) overstuffs a bear and it explodes, making an expectant little boy cry. The boy is the same one that Gru made cry with a popping balloon in the beginning of the first film.
In the scene where Lucy Wilde gives Gru a phone number to reach her, it is clearly visible as 626-584-5723. Calling that number reaches a recording of Kristen Wiig as Agent Lucy Wilde, with her outgoing voice mail message.
The actors are filmed the entire time they read their parts. Their facial and hand expressions are used on screen. Steve Carell's wife had fun pointing out the expressions in Gru that reminded her of Steve.
The start of the film features yellow-jacketed humans speaking a foreign language. This is a reference to the original design for Despicable Me's minions - the iconic shortened shape came about as a result of a low budget for the first film.
El Macho drinks a liquor bottle during a flashback scene. The label says "La Venganza del Escorpión", which is Spanish for "The Revenge of the Scorpion". Behind it there is a poster, also in Spanish, that reads "If you are drinking to forget, pay first."
When Gru first visits his Minions in the underground workshop, several Minions can be seen taking a break and eating lunch on top of a cross beam. This is in homage to the famous "Lunch atop a Skyscraper" photograph from 1932.
When the Minions assemble to give Dr. Nefario a 21-fart-gun salute, the bugle call "To the Color" can be heard playing in the background. This is a U.S. Army bugle call that is traditionally played on Army posts after the call of "Retreat," as the post flag is lowered at the end of the duty day.
There's a brief shot in the film in which Edith is playing ping pong with a minion, but uses a pair of nunchaku as opposed to a ping pong paddle. This is a reference to a famous Chinese Nokia commercial in which a Bruce Lee impersonator in a mock "lost home video" also plays a game of ping pong using only a pair of nunchaku.
In the scene when Anti-Villain League director Silas Ramsbottom shows Gru a video of a rabbit being injected with mutation serum, the name tag of the lead scientist in the video reads "COFFIN" - a reference to co-director Pierre Coffin, who also provided the voices of the Minions.