The fool is the opposite of the wise man. He just skips around in a giddy delirium all day, nattering on and on about whatever pops into his head. While the wise man sees the vanity of the world, the fool totally buys into it. The wise man is like someone who is able to see through the fog, while the fool is only blinded and confused by it. The wise man knows that he needs to occupy himself with work, but the fool is a slacker—probably hitting the Doritos and Fresca in a big way at high noon, while all the other laborers are working in the fields.
But unfortunately, being an idle, babbling fool just amounts to "consuming [your] own flesh" in the end (gross). Ecclesiastes writes, "For like the crackling of thorns under a pot, so is the laughter of fools; this also is vanity" (NRSV 7:6).