When Leandro Herrera lies beaten on the ground, he asks someone to call "Amberlamps". This is a reference to the viral video of Thomas Bruso (original inspiration of the Bad Ass movie duology), where a passenger who just have taken a beating from Russo, asks for an "Amberlamps". However, due to his impeded speech (presumably caused by the injury) and ambient background noises, his call for "an ambulance" was misheard by many as "an M&M" or "Amber Lamps."
When Frank and Bernie step out together for the first time to go after Manny's killer, they arrive at an apartment building. The entrance to the building has an access code intercom system keypad and a residence listing to the right. The residence names on the list are all recent (2013-2014) and former Seattle Seahawks players including Seattle Seahawks legend S. Largent (Steve Largent).
When Manny is sparring at the beginning of the movie, Frank is heard coaching him by saying to "work the body." Manny starts sending his shots lower and one of those punches lands below the belt. Manny's sparring partner can even be seen noticeably shaken up when he slightly doubles over momentarily after the low blow.
The trivia item below may give away important plot points.
At the beginning of the movie, when Adolfo is talking to Manny in the parking garage, Adolfo says, "I'd rather you stick a needle in my eye than insult me." Much later in the movie, when Frank confronts Adolfo in his home, Frank ends up sticking an ice pick into Adolfo's eye.