When Kevin Smith and Scott Mosier heard Alan Rickman was a Chasing Amy (1997) fan, they asked him to play Metatron. He read the script and came back with two questions, "Would they stay faithful to the script," and "Were the wings real or CGI?"
William Donohue of the Catholic League lambasted the film, and publicly protested against it for months, without actually seeing it. When his office called View Askew and requested a special screening so he could "speak about it intelligently," Kevin Smith responded "So what has he been doing the past six months?"
(at around 41 mins) The Mooby restaurant's playground was created especially for the movie - it's shaped like a giant meat grinder.
Jason Mewes had the entire script memorized before rehearsals. When asked why, he said it was because he didn't want to anger Alan Rickman, and because Kevin Smith took him aside before rehearsals began and said he needed to be on his best behavior and bring his A game to the set.
The hoods worn around the neck of the three angels in the film, Metatron (Alan Rickman), Bartleby (Ben Affleck), and Loki (Matt Damon) represent their haloes.
Bob Schreck, Joe Nozemack, Jim Mahfood: all as church parishioners. They all worked with Kevin Smith in comics, with Mahfood illustrating the Clerks comics, Schreck as editor on Kevin's Green Arrow run, and Schreck and Nozemack as co-publishers of his Clerks and Jay and Silent Bob Comics at Oni Press.
Kevin Smith: [Star Wars] (at around 32 mins) After meeting with Bethany, Jay says "It's like I'm Han, you're Chewie, she's Ben Kenobi and we're in that fucked-up bar!" The scene transitions are done in the same way as the Star Wars movies, wiping instead of just cutting to the next scene.
Kevin Smith: [comic books] One of the Stygian triplets wears a Hellboy t-shirt. Bartleby says, "You wouldn't like me when I'm angry.", in reference to The Incredible Hulk. Madman toys appear in the toy store.