You've seen the HappyOrNot kiosks all over the place, the 4 faces going from happy to angry. It's a quick and easy way to collect data in so many different environments, including airports.
According to HappyOrNot, with feedback from 4.5 million travelers at airports around the world, they've determined that Wednesday is the best day to fly because people are the happiest while Sunday is the worst because travelers are the least happy. They also say that flying around 8am is the best time and late night travel is the worst.
Remember this if you're booking a vacation this summer. Don't let your trip get ruined by angry people!