The opening minutes: Dante goes in to open the store, assuming it's going to be an ordinary day. He pulls up the metal shutters to find... the inside of the store is on fire. Dante promptly slams the shutters closed, looks around, then pulls the shutters up to confirm that no, his mind is not fucking with him, the inside of the store really is on fire.
And everything but the fire is in black and white.
Dante shoots him a look
Randal: ...I left the coffee pot on again, didn't I.
A real life, behind-the-scenes example: Jeff Anderson told the story on the DVD commentary of how he was staying during filming at a place that appears briefly in the background across the street, and sometimes after a long day he would end up unknowingly trudging back there with the "Porch Monkey 4 Life" shirt still on, thinking to himself how people in that neighborhood sure do like to throw a lot of bottles for some reason or other.
Another one from the commentary: Kevin Smith was talking about the different actresses he considered casting as Becky, which included Sarah Silverman, who allegedly said "Let me play Randal and I'll do it for free."
Randal taunting Elias by talking about "...the Beast we call the Desolate One! The First of the Fallen, the Spoiler of Virgins, the Master of Abortions! (grabs mike) Let me help you out of your chair, Grandma!!!"
Jay: GRANDMA! *climbs through drive-thru window* WHAT WAS IT LIKE TO BE ON THAT HOLIDAY SITE?!
When Dante tells Randall Becky is pregnant, he is too occupied playing with his card to care. When Dante tells him he is the father he drops his cards in shock, hitting a customer passing by causing him to front flip fall over a table.