You should read his original "secret origin" story! He's a slacker delivery boy for a professor who slips into a baseball game while working. Instead of drinking a bottle of soda he drinks the professor's super-rubber compound and becomes able to inflate and bounce!

I think MOST of the Legionairres were fashioned around a silly code-name that came first.
What?? Are you suggesting that "Matter-Eater Lad" as a code name was
silly?
I almost put in my post that I cant defend "Matter-Eater Lad"
Well, I held out as long as I could, so I'll chime in and mention that I'm waiting for the episode with bated breath. Geoff Johns writing the script gives me a fair amount of hope.
That said: for the record, Chuck Taine, the future Bouncing Boy, actually stopped off at a robot-gladiator tournament ("savage, exciting... yet harmless") rather than a ball game.
As for defending Matter-Eater Lad, I'll step right up. Matter-Eater Lad is 100% pure unadulterated awesome. He's basically a character who screams out to writers, "do something cool with me". Some, like Paul Levitz (who wrote some extremely great Legion stories, make no doubt), knew their limits and declined to take up the challenge. Others have bravely stepped up to the plate and given it their best, to varying degrees of success (Keith Giffen, aided and abetted by Tom and Mary Bierbaum, probably made the best go at it I can think of). Matter-Eater Lad is a heroic soul with a fantastic sense of humor, a better set of hand-to-hand combat skills than you might think, and the ability to thoroughly destroy any form of matter you'd care to name (albeit in a peculiar fashion). Even in the 90s pre-Zero Hour
Legionnaires series, when a lot of the Legionnaires traded up their Silver Age monikers for new Image-kewl names (Lightning Lad=Live Wire, Sun Boy=Inferno, Element Lad=Alchemist, Triplicate Girl=Triad, Phantom Girl=Apparition, etc. etc. etc.), our boy recognized that the name "Matter-Eater Lad" was simply too awesome to be improved upon. And he even saved the universe once, by eating the Miracle Machine--an object even Superboy couldn't destroy.
I'll defend M-E Lad with my dying breath. But I'm not the guy you should watch out for. As the saying goes, you don't want to pick on Matter-Eater Lad. Because being picked on gives him an appetite.
And you don't want to give him an appetite...
--g