The video game featured in the movie, Demonik (2006), was to be an actual video game that was to be released for the Xbox 360. The project was canceled when the production company Majesco Entertainment ran into financial troubles.
According to Nick Swardson in the pot smoking scene Dante was was given fake weed. Dante then decided to get his own weed. So for each retake of that scene he was lighting up real bong hits. Swardson stated that the actor after the takes said he "couldn't feel his legs" and that he needed to go to the hospital.
The game used in the movie, Eternal Death Slayer 3, is actually a modified version of Majesco's BloodRayne 2. Both BloodRayne 2 and the abandoned title Demonik were developed by Texas-based developer Terminal Reality.
When Grandma Lilly is outside gardening, Samantha pulls up in Kane's car. Lilly turns to talk to Samantha, the house behind her is the same house used as the Manor in Charmed. You can also see Grandma Lilly's house in Charmed. The last season of Charmed was filmed about the same time as Grandma's Boy was filmed.
When Alex comes out of Samantha's office J.P. is standing facing the wall and you can see a poster that says Gay Robot (2006), a TV-series written by Nick Swardson (Jeff) and a character from a sketch of the same name from Adam Sandler's 2004 comedy album "Shh... Don't Tell". There is also a small poster for "Gay Robot" on the shelf behind the desk in Mr. Cheezel's office.
During the climactic video game scene J.P. Attempts to insult Lilly by telling her that Murder, She Wrote (a TV show popular with senior citizens) is on. Doris Roberts (who played Lilly) appeared on 2 episodes of Murder, She Wrote.
The large white metal dividers in J.P.'s home with the repeating square and circle motif can also be seen as office decor when Renée Zellweger enters the "Now" magazine offices near the end of Down with Love (2003).
Shirley Jones and Shirley Knight were both nominated for the Academy Award for Best Supportinng Actress in 1961 with Shirley Jones winning the Award her only time nominated. Shirley Knight was nominated again in 1962, but did not win.