The U.N. has decreed it, and so it must be: Today is officially International Happiness Day. Which brings on the cynics, like the folks at the U.K.’s But think about it: Sometimes you do feel a rush of happiness that makes you want to burst into song—“Oh, What a Beautiful Mornin’,” or “Zip-a-Dee-Doo-Dah,” or “Feelin’ Groovy.” Not to mention “Chelsea Morning” and “What a Wonderful World.” What are the tunes that convey unalloyed joy to you?  We exclude “Happy Days Are Here Again” from contention; this anthem to political triumph is pure cynicism.