On your left! (Source)

There you go, dashing across town. You're careening through turns, flashing, trashing, and crashing your way through midtown like a blur of greased lightning on two wheels.

You're a bike messenger—part athlete, part courier, part crazy. People will call up the company you work for (or call you directly, if you're experienced with a pre-fab client list) and hire you to blast your bike through traffic to deliver everything from important documents to designer duds. Even Christmas trees are fair game (source).

You're like Spidey on a mission without the web slinging to fall back on. You'll bank on brute strength, navigational skills, and the ability to withstand a concussion, and still get back on the bike. Blood, scabs, and scars are your badges of honor.

You'll make a little more than minimum wage for the chance to put your life on the line riding forty to sixty miles a day.

Few jobs offer the thrill of a bike messenger. Even fewer offer the chance of being dismembered by a car door or flattened by a turning bus. Being a career courier is an extremely dangerous job that offers powerful calves and a killer cardio workout, in lieu of a living wage.

Bike messengers do the job because they love it.

You have to be in it for the excitement, the adrenaline—the rush. Being a courier is more about the lifestyle of the profession than most other jobs; it's fresh air, exercise, and nerves of steel mixed in with a generous dose of cuckoo for Cocoa Puffs.

Depending on where you work and the time of year, you could have plenty of down time. There are both part-time and full-time gigs available. Many couriers are also college students, and since you're paid per delivered piece, you usually have the freedom to schedule your own hours, and get time off when you need it.

That being said, there will be times of the year that you are slammed with work. You'll be riding ten to twelve hours a day, six days a week. You might be able to stockpile a healthy amount of money on those days. Maybe.

It doesn't hurt to have a thick mane of hair that whips back in the wind, either. (Source)

You'll need keen instincts, a good eye for squeezing in between vehicles, excellent knowledge of local shortcuts, and an overall fabulous sense of direction. Don't expect Siri to guide you there, unless you get her to speak very, very quickly.

You'll also need to be super speedy on that bike and in excellent physical shape. You'll be pedaling at sonic speeds all day long, so a good heart and strong legs are a must. Expect backaches, sore legs, and cramps, even if you're a top cyclist. This is a job for athletes who aren't afraid of pain.

You obviously need to love being outside and riding a bike. That means in both good and bad weather. Deliveries don't stop for rain or snow, and you won't have that cushy truck to keep you dry like UPS and mail carriers. It's just you and the road 24/7.

As for equipment: You'll need a good bike, extra inner tubes for when you get a flat (and you'd better know how to change one), a sturdy helmet, a bottomless messenger bag, a cell phone or call radio, cycling gloves, a really good bike lock, a backpack, and some really solid health insurance (usually not provided by the company you work for).

Surviving as a cyclist in a city, with important documents that have to be delivered on time, is like being a stray dog trying to cross a busy freeway, or a roach trying to survive in an obsessive-compulsive's kitchen—hazards are everywhere.

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