Obvious example: selling cigarettes.

The cigarette is the deadliest artefact in the history of human civilisation. [...] Cigarettes cause about one death per million smoked³⁵ with a latency of about 25 years, which is why the 6 trillion smoked in 1990 will cause about 6 million deaths in 2015. [...] One-third or one-quarter of those deaths will be from lung cancer; about one every 15 or 20 s. [...] Cigarette companies make about a penny in profit for every cigarette sold, or about US$10 000 for every million cigarettes purchased. Since there is one death for every million cigarettes sold (or smoked), a tobacco manufacturer will make about US$10 000 for every death caused by their products.

Presumably there are even worse legal ways to make a profit, but this sets a nicely unambiguous lower bound, I think.

End of life treatment.

Extending the literally worst part of most people's lives for as long as you can, to the tune of over 20% of medical spending in the US.

Patent trolling?

Gold mining. Adding marginal ounces of gold to world supply adds very little utility because gold can be pretty much endlessly reused and there is plenty of it around that has already been mined. Central banks of fiat currencies sit on many years supply for no particularly good reason. Meanwhile, the industry consumes $billions annually of real resources (like fossil fuels and capital equipment) and produce pollution and environmental damage.

I recently read Peter Leeson's paper, Better Off Stateless: Somalia Before and After Government Collapse, which argues that Somalia's government was so awful that anarchy was actually better in most of the ways we care about. It has an example of a profit-making enterprise with negative value:

Under government, a great deal of Somali production was military hardware that citizens did not consume. In fact, to the extent that this hardware was used to suppress the Somali population, this sizeable portion of pre-1991 GDP was actually negative value added from the perspective of citizens’ welfare

...

[Military spending] left few resources for investment in public goods, like education, health, or transportation infrastructure...[In 1990,] government spent less than one percent of GDP on economic and social services, while military and administration consumed 90 percent of the state’s total recurrent expenditure

So, weapons manufacturing for an evil regime seems like a candidate for effective malice.

One possibility is computer games, e.g. I've certainly lost a good chunk of hours to the game Diablo. Modern things like Farmville seem especially pernicious. [This is not to be construed as all gaming is bad, etc.]

The problem with vice-type industries like gambling, cigarettes, and junk food is that one can make a reasonable argument that the users are deriving some kind of utility from gambling, smoking, and stuffing their faces with Cheetos. How do you measure utility? If it's strictly in terms of WTP (willingness-to-pay), then vice doesn't seem to be such a good candidate, you need to look at industries where there is an element of force or fraud, but not so extreme that the industry is banned.

Also one needs to distinguish between utility at an individual level and utility at a societal level. In arms race type situations, things which have a lot of utility at an individual level have very little utility when you look at things from the perspective of the entire universe of consumers.

That said, my vote is for higher education. At an individual level, lots of bright people go deep into debt and waste the best years of their lives because they are led to believe they will get good jobs which never materialize. At a societal level, a large portion of higher education is basically arms-racing, also known as credential inflation.

One could object that most higher education is performed by non-profitmaking institutions, but I think that is a legalistic limit on the definition of "profit" which is not true to the spirit of the question. Universities and professional schools generally do very well and pay their senior management very handsomely.

Your question makes me think of what economists call negative externalities. Wikipedia has a list of them

Homeopathy and naturopathic health cures. The only argument for these is that they work as well as a placebo.

Cosmetics and jewelery. These are particularly expensive mate attraction and social standing boosters.

Lobbying for government handouts/boons/subsidies. These have the potential to have net utility, but in many cases do not.

Monopoly businesses. Net loss of utility through inefficiency.

And finally, an overarching overemphasis on reliability. By declaring that 'failure is not an option', we spend vastly more resources than if we were to simply accept failure as an option and properly handle the failure cases. The best direct examples of this come from information theory: it is almost always cheaper to add error correction to reduce the error rate on a channel, than it is to improve a channel to reduce the error rate without error correction.

Are we trying to maximize profit or utility loss?

Getting governments to change laws to protect your profits. A classic example of this is taxi cartels, enforced by medallion systems - it's bad for cabbies, astonishingly bad for users, not great for new entrants to the system(and bankruptcy-inducing if they ever unwind the system), but the guys who paid a hundred bucks for a medallion in 1950 and sell them for half a million today earned a gargantuan profit for no good reason except regulatory capture.

Operating casinos? They're fairly harmless to most people, but gambling addiction has destroyed people's lives.

Factory farming.