Every comedian knows that a joke that kills in one room can die in another. It's rare to laugh out loud at a comedy record when you're listening at home even though the people in the room are guffawing. And the opposite is true too: A comic who's only so-so on TV or on a CD can be a riot live.
It all depends on the setting. Are there other people around? Does the room have energy? Are people warmed up? Is it a lively group? Etc. One interesting thing I've noted is listening/watching a comic at home with even just one or two other people leads to a lot more laughter than if you're alone.
What's So Funny? Well, Maybe Nothing (NY Times) is a scientific look at why people laugh. Turns out "funny" has less to do with laughter than a lot of people think. And the results are definitely interesting from a standup perspective.
According to the article, people use laughter as a punctuation mark. It's an exclamation point, a gasp, an a-ha, a recognition, a conversational lubricant like nodding or saying, "uh huh."
He found that most speakers, particularly women, did more laughing than their listeners, using the laughs as punctuation for their sentences. It's a largely involuntary process. People can consciously suppress laughs, but few can make themselves laugh convincingly.
I think that last part is interesting too: You can't fake laughter convincingly. That's part of the whole rawness of comedy. An audience can pretend to like a band or a painting, but it's pretty obvious when people are fake laughing. You're either on the bus or off the bus.
Also, we laugh as a way to connect.
The brain has ancient wiring to produce laughter so that young animals learn to play with one another. The laughter stimulates euphoria circuits in the brain and also reassures the other animals that they're playing, not fighting.
Playing, not fighting. That's why comics can get away with saying some of the meanest and/or most truthful things, because they do it in a playful way. They can deliver straight, painful medicine because the pill is coated with sugar. It's amazing what you can get away with saying as long as people are laughing.
There are also a lot of control/hierarchy issues in play.
[Laughter is] a subtle social lubricant. It's a way to make friends and also make clear who belongs where in the status hierarchy...[From an experiment:] When the woman watching was the boss, she didn't laugh much at the muffin joke. But when she was the underling or a co-worker, she laughed much more, even though the joke-teller wasn't in the room to see her. When you're low in the status hierarchy, you need all the allies you can find, so apparently you're primed to chuckle at anything even if it doesn't do you any immediate good.
So people laugh at others who they perceive to have higher status. That's why control is such a big part of standup. If you lose control of the room, forget about it. If they don't respect you, they'll never laugh.
But what about Rodney Dangerfield, king of "no respect"? That's bullshit schtick. Listen to an album of his and you can see he's got the whole room in the palm of his hand. Total master at controlling the room. No respect, my ass.
Actually, that's a common comic ploy, insult yourself as a way to ingratiate yourself with the audience. Then once they've "let you in," ya take 'em over.