Or, at the very least, "Camptown Races."
A blues staple since its birth (originally used by slaves as a means for their own creative expression), rockers such as Bob Dylan, Neil Young, and The Beatles helped introduce it to other audiences. It's also a surprisingly complicated instrument to learn. Its deceivingly simple appearance makes it seem as if just anyone can pick it up and blow out a tune. Little do they know it takes a solid four hours of practice before that can happen!
Actually, the only reason it's easier for most people to learn is that it's so convenient it can be played and practiced no matter what the person is doing. On their lunch break, during their commute, surfing the web, or even making love. This is where the harmonica player in training has a definite advantage over, we'll say, the pipe organist. While he may manage to play this pipe organ of his during his commute (you never know, traffic may just be that bad), he'd never get away with playing it during intercourse (as if a pipe organist would ever get the chance for that anyway). Not that a harmonica player in training would "get away with playing it" per se, but the look on her face as he sucks and blows out the first few bars of "Sixteen Tons" is priceless.
If you'd like the learn to play the harmonica, buy one. Listen to lots of Bob Dylan. Drink some root beer, too. This won't help you learn any quicker, but boy oh boy is that stuff good.
Pick it up and stick it deep in your mouth (no, the wide end, you sicko). Blow on the five, suck on the four. Blow on the five, suck on the four. Doo-dah. Doo-dah.
If you wish to learn anything more advanced in the way of "harping," just experiment on your own. It's a fine little instrument to learn by one's self, and before he knows it he'll be raking in nickels in the subway just like a professional vagrant!