Garfield, that cartographer of barren landscapes of human existence, takes aim at anyone who thinks they can accomplish anything, achieve the smallest triumph, or even occupy their time in any meaningful way. Jon deludes himself and tries to lie to his cat (who is having none of it), that not only will his life be imbued with meaning by completion of tasks, but that he has such important occupations ahead of him. The enthusiasm of this announcement is perhaps the saddest, funniest thing in the strip, unless it's Garfield's knowing acceptance of an essentially empty existence in panel two. Only in Garfield is sloth to the point of pride in avoidance of any movement or responsibility equated with a kind of Zen perfection.
Garfield's assurance that the lowliest of human behaviors qualifies as an activity worth consideration is not totally inaccurate, but holds no comfort for Jon, who was surely looking for a way to inscribe positive meaning on his day. Now he has to look in the mirror and say "all I did today was lie to my cat, who didn't believe me in the first place." Confessing your shortcomings also counts as doing something.