An underachiever or irritatingly laid-back character.
Possibly disorganised, possibly prone to procrastination.
There can be a bit more to it than mere laziness or sloppiness, a perception that the rat race isn't worth it and shop-till-you-drop a surrogate happiness of low quality, and a slow poison, too. So this kind of slacker might (or might not) be dedicated to what he or she does (paragliding, for example), but would probably not list “climbing the corporate ladder” as an ambition or “shopping” as a hobby. May be a bit of a “Generation X” thing.
Hear Beck's song “Loser” or see the video for Soundgarden's “Black Hole Sun”.
I mean, most of the girls I went to school with were crazy about buying all kinds of stuff and they would disappear in shoe shops for days, but list “shopping” as a hobby? No one would have thought of it as a damn “hobby”! And even if someone had, they still wouldn't have dared to admit they're so damn shallow. What has the world come to?
G: “Yeah, I know. Nothing to be done about that. The shits are doomed and so are we. You should see their parents. Now get off your butt and out of the car, you little slacker, we still need to get groceries.”
Imma slacker, never did I have a lot of dough
Imma slacker, smoking pot and watchin' videos
Imma slacker, go whichever way the wind blows
Those just tuning in I'm just letting' ya know
Imma slacker, every time I take a look around
Imma slacker, stuck upon my face is a frown
I don't do enough, I just fool around
Ya'll can go to hell, how does that sound
from Slacker by Tech n9ne