During the Shaming The Mob scene, Alvin says emotionally, "You should all be ashamed!" and points at random people in the crowd before adding, "How dare you!" What makes this funny is that this is Alvin, school bully, sounding like a prissy middle-aged lady.
When Mitch gears it, leaving the six voiceless zombies (bonus point on one of them coughing) in smoke, and their reaction when they see Judge Hopkinks hanging on the speeding van for dear afterlife. It's even funnier when you realize in life the fastest thing they probably ever encountered was a horse drawn carriage, which also explains why that one zombie just stood there, staring at the van before it ran him over. No wonder the Judge was screaming.
Alvin trying to impress the ladies with his sweet dance moves.
Mitch: You're not freeze framing mom's exercise DVDs, are you?
Neil: No. (The next shot shows he's doing exactly that)
"Do I look crazy to you?" *goofy grin*
Towards the beginning of the film, after the students sing a song in a school play, the audience claps, however one guy cries out "You Suck!"
The song in question is also Season of the Witch by Donovan.
When the angry mob makes their way to town hall, Mitch thinks it's the zombies at first. The following is pretty hilarious:
Mitch: I think it's the zombies.
Mitch: No, it's just grown-ups.
'Alvin:(with more fear): Hide!!
Earlier in that same scene, Neil was pretty proud of himself for reading twenty six pages in a book.
The zombie movie Norman watches in the opening has the actress look at the camera with annoyance when the zombie actor moves too slow, and then she pushes the boom mic away while screaming.