So the answer to this question lies within the mechanics of the initial Slacker skill -- Tool Around.
This is a zero MP ability that... appears to do nothing.
Ah, but that is where you are wrong, reader! Tool Around simply starts off by doing nothing. But the more you Tool Around (Or the higher your slacker level, at any rate), the less chance you have to "Do Nothing", and use one of the other slacker skills instead!
We're talking many, many levels (nigh 40), mind, but in due time, you can have your slacker cast powerful spells, including med. damage all, strong heal all, and status cure all, all at Lady Luck's whim. Or you can simply "Do Nothing" again, that option never fully goes away, I've found.
But the important thing to note here, is that Tool Around costs 0 mana. So on a character where you are trying to store up mana for a more powerful ability, Tooling Around might prove more effective than weakly flailing with a basic attack. (Or it might not. Again, it's random)
So to unlock your full slacking potential:
- Tool Around as much as possible (because why not!)
- Tool Around while waiting to use your other abilities (Dammit, Jim, I'm a slacker not a flesh-restoring doctor)
- Live up to the Pin your mother always knew you could be, you 34-year-old live-in!