Jon has a plan to make Garfield feel bad about himself, and he wants you to be a part of it! There's usually a reason Garfield breaks the 4th wall. Today that reason is to make sure you know where the green shirt came from. Imagine how freaked-out you'd be if the shirt suddenly materialized on Garfield's body.
The punchline, of course, is not that Garfield is semi-literate, because we witness his reading abilities all the time. No, our pudgy hero is having what may be termed "hysterical illiteracy", a condition hitherto unknown in the annals of medicine. Hitherto unseen in the annals of fashion is the LAZY shirt, which Jon must have made himself. While Old Navy will happily supply those children of roughly Garfield's figure with shirts reading FLIRT and CHICK MAGNET, nothing so brutally honest will grace the torsos of our youth. Why does America love Garfield, when he exists to remind them of their worst foibles and tragedy of their alienation? Answer: We hate ourselves!
Special thanks to the God-among-sarcastic-comics blogs, Comics Curmudgeon for linking to us (me?). May the heavens rain lasagna upon Josh... even though he doesn't like Garfield and is rude about it all the time.