THE ABCs OF A-Bs
There's only one hard and fast rule for A-Bs, if not life in general: Funny First. Joel and Leah first articulated this ABsolute to me, and I agree. If you laugh at it, a lot, it must be a good A-B. If you leave the A-B looping on your DVD player while you're at work just so you can turn the TV on when you get home and see it running for you, like your dog runs to you, then it must be good. Actually, I have a cat.
But there are certain things. Keeping it short is a good idea. There's no need for even a second of downtime, even though that downtime toward the B-end can set up the effective startle of the A-end.
Violence and Volume work. Surprising, ridiculous behavior. And sexual innuendo, or outuendo. A-Bs are really ABout outbursts. Art is a mirror--you see something outrageous, and you react outrageously.
A-Bs typically feature over-the-top, cartoon-like behavior; this is why actual cartoons rarely work for A-Bs. In animation, literally anything can be depicted; you expect the unexpected, so the element of surprise is gone. Stick to live-action. For example, the animated classic The Grinch Who Stole Christmas is not a strong source for A-Bs. On the other hand, the live-action ABomination featuring Jim Carrey is an A-B smorgasbord. Jim Carrey's parents should have named him "A-B," he casts such a giant shadow over the art form.
EGGHEAD THEORETICAL HOOEY!
One approach to assessing why a work of art has quality can be found in David Bordwell & Kristin Thompson's textbook Film Art: An Introduction (McGraw-Hill, now in its 10th edition). The authors offer four criteria for evaluating the depth and merit of an artwork: complexity, originality, coherence, and intensity of effect. Note that this is not an argument about taste--you can like whatever you want. This is about being able to agree on what we can judge as good, not what necessarily pleases us. We're talking about judgment, not taste. I fucking love cheeseburgers--that doesn't mean I'd claim they're healthy. Likewise, I would never say that Eminem is a bad rapper--I just can't fucking stand him, and he can go fuck himself.
A good A-B leans mostly on intensity of effect--if that's not there, it's probably not entertaining. But originality and coherence are crucial too. An A-B that has coherence seems balanced--the beginning and the end enhance each other. An A-B by definition is a bookended segment; that's what the A and the B are, for Christ's sake. And like a Möbius strip, they join together, so the B becomes the A, and the A the B. What the fuck was I talking about?