Honestly, I think Costa Ricans *are* really happy. Maybe it's that Latin bonus thing, at least partially. But here are a few other possible reasons why it's just awesome being Tico:
1. Costa Ricans are very socialist with their health care, education, transport, and housing. You're taken care of. People abuse the system, sure, but hardly anyone is against socialized medicine (keep in mind that excellent private care is available to folks with money, though they still pay for guaranteed basic coverage). So people aren't stressed about losing everything because grandma gets cancer.
2. Costa Ricans are very socially liberal. They're probably going to legalize gay marriage, prostitution is legal, guns are legal, drugs and abortion are technically illegal but rarely prosecuted, traffic laws are free-form, the press is probably freer than the USA's. So people aren't stressed about some morality police breathing down their necks, like in the Middle East.
3. They live in Costa Rica.

4. They eat really healthy and exercise *a lot.* None of that fried pork with tortillas, cheese and beer, like Mexico. Which is sort of a tragedy, if you like Mexican food, but in the long run healthy people are happier. Think Northern California or Colorado.
5. The gap between rich and poor is big enough to allow large private investments - for instance, their huge pineapple and coffee plantations, which are impossible where '60s-style land reforms limit property size. But that gap is much narrower than in other Latin America countries, there's an actual middle class. Why bother having a class war if everyone's pretty happy with the current distribution of wealth?

6. Being the most democratic, ecologically sound country in the hemisphere is a tremendous source of pride, and smugness. But it's undeniably awesome. Brazil has soccer, the USA has freedom, France has haute cuisine... and Costa Rica has rainforests. Almost 30% of the country protected from development. I've watched the government shut down two five-star Occidental properties at the height of high season because they were dumping waste in a coral reef. I've seen them shut down a gold mine. And protect sloths, baby sea turtles. 857 species of bird (more than Europe), a quarter of the world's bees, etc etc...that's just cool. Best of all, they proved that even a poor little country could do it; who here can say their country has fewer resources than Costa Rica? Not many. If you're going to have a superiority complex, it might as well be about saving the rainforest using ingenuity, savvy advertising, and greatest zip line canopy tours in the world.
