It's not nearly as simple as that. True, people can always be found to "demand" that the USA "do something". But then, people can always be found to demand that any government "do something". Often that "something" turns out to be profitable for the people who do the demanding. But whether the loud demands are at all representative of what people in general want... that's a different question.
The USA is supposed to fund UN peacekeeping missions - actually, a very inexpensive commitment compared to fighting wars - because all the 193 member nations do so. Likewise with other routine UN functions. Please note that the US government was instrumental and took a leadership role in setting up the UN, which is why its headquarters is in New York. Many of us would prefer it to be in a different, preferably small and non-aligned nation.
The anti-pirate patrols are much appreciated and have done a lot of good. However, there is a strong argument that local nations should indeed perform that role instead; that way they would be more inclined to address the root causes of piracy.
I don't believe anyone ever demanded that the USA become the "World Police", and your rude comment about Europeans is wholly unjustified. Indeed, a study of history suggests that it was far more the choice of Americans and their government to occupy Europe (and Japan) than that of the locals. Of course, as of 1945 the USA was the world's wealthiest and most powerful nation, having remained neutral for the first two years and three months of WW2 in Europe. Thus, when WW2 ended, the USA was the only major nation whose own territory had not been invaded or bombed. Germany was shattered and decimated. Italy was little better. The USSR had lost one in seven of all its people - soldiers and civilians - over 25 million dead. Britain had not suffered so many deaths, but was utterly bankrupt due to the cost of fighting both world wars. (The UK finished repaying its war debts to the USA in 2006).
Under the circumstances, I find the expression "lazy f'kers in Europe" extremely offensive and unfair.