Lazy, thoughtless, irresponsible, drunk, easily pulled in by ridiculous shiny things.
Homer is a distilled archetype of a thousand jokes about men, some affectionate, some vicious, being played for laughs. He, and other characters like him, are one of the gender archetypes that we share with one another about "What men are often like".
Of course, there are some men who act an awful lot like Homer and his onscreen ilk some or much of the time. That's what makes it funny. That's what makes it okay, right? It's fun for us to show off this kind of thing as a core male archetype, because it's true!
There is a big difference between the Homeric state (snerk) in reality and in the show:
Homer is the way he is all the way through; his internal voice has a place in the show, and it's just as dopey as the rest of his behaviour. In reality, men aren't like that - or at least, very few of us are.
When men engage in this kind of behaviour, it's because we've decided to relax into it, or decided to hide behind it. It's easy to disavow responsibility, bounce around between dead-end projects, and stop caring about others.
And after, when a guy doing this kind of thing gets called on it, Homer's right there. We can make a few jokes about how dumb we are, we can hide behind Homer. We can say "Oh, I'm dumb; but that's okay because men are dumb."
We can convince everyone around you that all those jokes about Homer are true. We can participate in painting our entire gender as clownish morons. Because, see, it'll get us off the hook for whatever selfish thing we just did; it'll mean that we won't need to deal with the responsibility for it that's just been pointed at us.
So, we do, sometimes. That's a big, big part of what keeps Homer alive, keeps him current; the fact that we choose to participate in the image. He's a useful lie to have around.
Homer's not the only image like this. And, guys, we're not the only ones doing it. But we sure are doing it.
Gender archetypes make liars of us all.
