About once a week I come across it. Someone may be referring to a historical fact, or to a mathematical concept, or to famous scientific experiment, or to a...well, you get the point. Someone will be referring to something that they had been required to learn in school, laugh derisively, and say "well, I don't need that now that I am out of high school!" with the sub-text pretty much always being that learning the information, process, or concept in question was a waste of time and not applicable to "the real world."
The "I don't need that now that I'm out of high school" line is nothing more than a proud proclamation of intentional ignorance. If you want to know why out country is in a shambles, stop looking for conservative or liberal boogeymen, stop looking at religious or sexual minorities. Start looking at the fact that we are a nation full of people proud of the fact that we don't retain basic information once we have a diploma in hand.
Once I have heard someone say that they don't need some skill or information or ability post-school, I have a very hard time taking anything else they say about any subject seriously.
Leaving aside the very real fact that, now that we don't live in a society where young men automatically go to work at dad's factory and young women are usually married and pregnant at 19, learning all of these "useless" facts and skills opens up the possibility that a young person can actually find a career path; leaving aside the fact that there is a pleasure in learning this information for those who go with it rather than resist it because to do so is somehow perversely considered cool; leaving aside the fact that simply having been exposed to this sort of information can provide one with an appreciation for the work lives of others who are not in one's own occupation, and therefore make it easier ot live with other people; leaving all of those very valid reasons why it is a good thing to have learned and been exposed to a wide range of academic disciplines, the claim that what one learned in high school (or junior high, or college) was a waste of time best left to nerds and egg-heads and not applicable to the so-called "real world" remains complete and utter bullshit.
Let's take a common high school math class: algebra.
Algebra, on it's surface, seems to have very limited application to the non-academic world. If you are a construction contractor or involved in some types of business, you may have some use for very basic algebra in order to solve day-to-day problems. But, all of those quadratic equations and discussions of arithmetic properties, what good is that? Well, it is true that you can get by, day-to-day in most jobs without having to make use of those skills and knowledge sets. In that sense, you don't need it. But that doesn't mean that it isn't useful. Go here to see some places where quadratic equations come up in your everyday life, even if you don't do the math, knowing that it's there can help you make sense out of what's going on. Even if you don't need ot solve for them, you can find uses that will allow you to improve your life, and likely improve your workplace, by retaining this knowledge. You may not need it, in the same way that you don't need a cell phone - it's still useful to have one, and the more you use it, the more likely you will be to find further uses.
How about another math class: statistics.
This one tends to be even more poorly understood, and in my experience even more likely to be scoffed at by the proud ignorance brigade. You can probably go on with life quite well without being able to perform a chi-square test, or calculate standard deviation on the fly. However, if you have learned to do these things at some point, and retained a decent part of the conceptual knowledge, you are far, far, far less likely to be conned or scammed than everyone else around you. Simply remembering that there are ways to determine whether or not a correlation is due to random chance or due to causal factors allows you to ask some important questions when a politician pushes a policy, or when a scam treatment is presented to you, or when someone wants you to buy something to increase your fuel mileage, or when a self-help guru is trying to peddle idiocy packaged as wisdom (I'm going to go out an a limb here and guess that The Secret didn't sell well amongst mathematicians). In other words, having just a basic-level knowledge of statistics, the sort that someone could acquire from high school and retain through adult life, will make you a smarter consumer, voter, and citizen. Again, can you get by in life without this? Yes, you can live day-to-day without basic mathematical knowledge, but much of the poor policy passed by politicians and the idiocy marketed to consumers relies on the fact that most people will relegate statistics to the dust pile of their personal histories and not use it to defend themselves as adults.
Let's look at something that is not as clearly related to day-to-day life and yet very important: history and civics classes.
I live in California, and like many states in the U.S., we have a referendum system that allows voters to put legislation onto the ballots and vote for it, bypassing the state legislature. On the surface this sounds great - direct power from the people, for the people, right? In practice, it means that many pieces of legislation get passed because they sound good to the public but make very little sense, are unenforceable or would require a wide range of inoffensive activities to become crimes, laws get passed that drain the public treasury for very little gain, or laws get passed that are struck down immediately (often in costly legal battles) because they clearly violate the federal or state constitution and therefore should never have been passed (and initiatives favored by both the political right and left do these things with what appears to be equal resolve and gusto, so don't go blaming the other side, your side is also at fault). Likewise, everytime I see someone who is swayed by cries of "activist judges" I know that I am looking at someone who doesn't remember high school history/civics and who therefore is being taken advantage of by political opportunists.
Here's the thing - if voters were generally more aware of what the constitution actually says (and right now I know that both Occupy people and Tea Party people are nodding their heads while dellusionaly believing that their take on the constitution is the only valid one...and both are wrong), then laws violating it (and wasting resources as a result) wouldn't get passed. If voters had a better idea of history, then they would know where to look in trying to figure out whether a proposed piece of legislation was likely to do what it said (after all, most of these measures have been, in some form or another, tried somewhere before). In short, knowing some basic civics lessons and retaining at least a broad outline of history (allowing for a small bit of research when necessary) would make us better voters.
The same sorts of things can be drawn from high-school level biology, physics, chemistry, even classes such as literature, art, and music. There is information and skills that can be gleaned from these classes which will help you to avoid getting ripped off, which will help you to avoid making stupid choices in the voting booth, which will help you to deal with many day-to-day matters. But, here's the catch, you have to come to the realization that "I don't need that after high school" is the battle cry of the imbecile. It's justification for laziness, not a show of wisdom or worldliness.