Competitive eaters have done it. A few brave amateurs have done it. If you're going to do it, though, you may want to bring some friends. Assignment #77 in the 365 Things to Do in Memphis is to take the Kookamonga Challenge.
You'll find the Kookamonga Burger at the Kooky Canuck on Second St. downtown. It's 4 lbs of ground chuck topped with 3 lbs. of bun, cheese, lettuce, tomato, onions and pickles. It has 12,387 calories. And if you can eat the whole thing in one hour, you don't have to pay for it.
I took the challenge last year (albeit with friends), and the anticipation of eating the giant burger was way worse than the actual eating. We finished in less than an hour, but it wasn't exactly easy. Pro tip: Call and order the burger ahead of time. Otherwise, you'll be waiting a while.