If laughter's the best medicine, you'll want to know whether you're handing out placebos. And that's one of the (relatively few) drawbacks of having really polite, encouraging friends—if they pretend to laugh at your unfunny jokes, you'll lose access to the cues that tell you whether your jokes are funny. So you should hang out with more jerks, right?
Here's a less radical solution: look into the work of UCLA researcher Greg Bryant, who says fake laughs are only convincing to strangers about a third of the time (and may be much less convincing to people who actually know you). And this makes sense, because there's nothing dignified or intentional about an honest belly laugh—much of the appeal of making people comes from the fact that it disrupts our social facades and forces us to reveal something genuine. A real laugh is about as calculated as a sneeze. SciShow's Hank Green walks us through gelotology, the science of laughter, in about four minutes:
But what if you're the one pretending to laugh? With hours of practice, you can probably make calculated polite laughter sound more like the real thing—but you're never going to fool as many people as you think you do. As we found out with subconscious lie detection, people tend to pick up on nonverbal cues relating to intention and then do nothing with that information unless they're actually answering questions in a controlled laboratory setting.