What does the expression, "nothing better to do" mean in a metaphorical sense? The definitions are clear enough. But the whole (phrase) seems to be greater than its parts (words).
closed as not a real question by StoneyB, Andrew Leach♦, MετάEd, RegDwigнt♦ Oct 19 '12 at 9:15
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If, for instance, one is being asked (or intimidated) to volunteer, its meaning is literal. One might respond sincerely (or sardonically): That's okay, I have nothing better to do.
On the other hand, when spoken about another person (usually derisively about a third party to a second or (silently) to a first party, its purposed meaning can be opposite of its literal meaning.
To say that another has nothing better to do in that vein, is to denigrate that person's use, or preferential use, of their own time, especially when such use is deemed to be either or any of inept, unwise, unfair, ill-considered, harmful, and the like.
For example, of a person plays bridge incessantly but never gains profit or acclaim, it could be said of her that she's got nothing better to do. The tone of such use is not uncommonly sarcastic, or piteous, but need not be either.
Nothing better rarely retains its literal meaning, just like the greatest thing since sliced bread doesn't really mean that absolutely nothing better has come along since the advent of the bread slicer – not the microprocessor, not the space shuttle, not the nuclear submarine. Consider Bob's answer to Rob, after he finds out Bob attended a panned movie:
It's highly unlikely that Bob literally means he couldn't think of any better use of his time, or that helping a charitable cause wouldn't have been a more worthwhile or noble time investment. He simply means there was nothing else on his schedule, so, even though he knew the movie might not be very good, he attended anyway.
By the way, putting too much literal meaning into phrases like "nothing better" can lead to logical fallacies, like this proof, which explains why a ham sandwich is better than true happiness:
As a footnote, there probably are a few contexts where "nothing better" literally means "nothing better," but I'd expect such usages to be narrow and well-defined. For example, from a scientific journal: