This could be an interesting exercise, but posting actual answers in a public forum would be an extremely stupid idea. Please do not do that.

The way you formulated a question is not conducive to getting the answers you want, because people start thinking of something along the lines of the Holocaust, 9/11, or other memes associated with evil.

I recommend rephrasing it as follows: point out the most anti-altruistic legal ways a person or an organization have spent $1M. Thinking about it this way, there is no shortage of examples, none resulting in Kawoomba losing much sleep. In fact, a large chunk of what most governments do is both legal and anti-altruistic.

For example, suppressing one's right to die with dignity, and thus forcing doctors and nurses to torture thousands of helpless and elderly people against their will, often for years, before they are allowed to finally die, is arguably legal, anti-altruistic and doesn't cost a lot to perpetuate. The resulting disutility by most measures outweighs 9/11 by many orders of magnitude.

Another example: resisting self-driving car adoption. This one is even worse, given that every year self-driving cars are delayed, costs about 30,000 lives in the US only.

Just look around you, money is spent in anti-altruistic ways all the time.

I have to say i don't get why so many of the comments on this are negative. Surely, if there was a completely legal way to inflict great harm on humanity for only $1Million then there are a ton of people/groups with the desire and resources to do those things. The idea that anyone with the desire to implement these things will learn about them first on LessWrong seems ludicrous to me.

Anyway, here is an idea:

1. Offer a $1Million prize for a working self-improving paper-clip maximizing AI. I think that this is very unlikely to produce anything, but since it is a prize you don't have to actually pay it out until someone builds a UFAI that destroys the universe. If no one seems to be working on it, you can always rescind the prize and move on to another evil scheme. I guess the downside would be if somebody accidentally made a friendly AI while trying to win the prize.

A relatively tame one: make a huge number of tiny donations to effective charities. Donations small enough that they cost more to process than they're worth:

The most extreme case I've seen, from my days working at a nonprofit, was an elderly man who sent $3 checks to 75 charities. Since it costs more than that to process a donation, this poor guy was spending $225 to take money from his favorite organizations. -- GivingGladly

Start a foundation which would support the teaching of fundamentalist religious science far beyond the confines of religious schools. So create I would seek out brilliant but deluded "values" supporting people and point out how this would reach far more people than they could ever reach by participating only within declared religious institutions. I would include teaching communist and anarchist "theories" of economics, especially including teaching that all successful corporations and the people who help them succeed are greedy and evil. I would set the foundation up so that it would be a pure meritocracy with fantastic status rewards for very capable and very intelligent proponents of the ludicrous crypto-religious positions I was advocating. I would concentrate the foundation in the newly developing countries where the cost of pulling capable of people in to my endeavour would be relatively low, and the impact of doing so would be relatively high, for example I would certainly wish to revive religious feelings in India in such a way to encourage governments go unliberalize their freeer market laws and to encourage intelligent kids from somewhat traditionally religious families to particpate in a resurgence of their traditional religions, especially their teachings against science and efficient economies.

Its possible we might identify some organizations that are already doing this with great energy and talent, in which case I would encourage joining forces with these organizations, possibly giving direct resource help.

Another idea: One of the great anti-utilitarian movements of our time has been the anti-vaccine movement. In that vain, how about setting up an anti-bed net advocacy group to argue that the children of Africa are being poisoned by chemical laden bed nets, and a charity that will collect and dispose of bed nets that are currently in use in Africa. I'm sure there must be a celebrity that would endorse such a charity. Snookie hasn't been doing much lately!

Longer-term idea, for those who don't believe in the efficient markets hypothesis: hire prostitutes (legal-ish in my country) to seduce promising young mathematicians and theoretical physicists, both to directly lead them to work less hard, and to encourage them to switch into higher-paying professions, so that we end up with basic research being done by less skilled people.

Finance is where the actions of a few individuals have the biggest impact on world utility, right? So we just need a way to compromise their decisionmaking. I think the cheapest way to achieve this would be to run some kind of macho-culture events for financiers, promoting ideas like "staying up all night makes you manlier" and "real bankers drink four shots on their way into the office". Better still, make these things be charity events (charity awake-a-thon anyone?) - spend a small portion of the proceeds on ineffective charity, and reinvest the rest into running more events.

I intend to bring utopia to the universe which will give an infinite number of sentient creatures an infinite amount of positive utility. Nothing can possibly be better than what I will do. But (for reasons you could not possibly understand) if given all the money I won't implement my plan. True, from your viewpoint the probability of my telling the truth is small, but

On 9/11, anyone know if the hijackers had actually modeled the building fire so that they knew they could bring down the building?

My impression is that they just got lucky, but I've never heard any facts on the point.