Why didn't the world community bake me a birthday cake? (or stop Mugabe, or Bush, or Chavez, or whoever)?
Example 1, Example 2
Many questions include an implicit assumption of agency that is fallacious. There is no world community - at least not a world community with an executive and a club that can be used to punish people or to bake birthday cakes. If you ask a question of the form "Why didn't X do Y?" then doublecheck to make sure that X is a real actor. Doublecheck that X has the power to do Y.
What is the consensus of historians on... (this picture of my goldfish)?
If there is in fact a secret cabal of historians that dictates opinions on history, nobody has informed me of it. This isn't actually a question, this is an invitation to debate, and not appropriate for H:SE.
Stop; don't go any further unless you think it through.. Example 1, Example 2, Example 3.
If your question begins "How many....", you're probably asking for a list, and you shouldn't ask that here. There are exceptions - "How many years did the 1812 war last?", or "How many patents did G. W. Carver have?.
Double check that you're asking for a "closed answer" - an answer, not a list. Then see if there is a way to rephrase the question so that it is really what you want. Sometimes this question is phrased as "What were the ... names of people on the Titanic?"
When did you stop beating your wife? (e.g. What is the timeframe for adam and eve?)
There are two problems with these questions. First, the timeframe isn't mentioned. If you're asking about behavior X in Roman History, the answer is generally meaningless unless you specify what period of Roman History. "What is the role of a censor in Roman government?" Depends on whether we're talking empire, republic, late empire, or June 7, 45 BCE. "Who is the Secretary of State?" Depends on which administration, and which year.
The other problem is questions that rely on assumptions - like the assumption that I beat my wife, or that I'm married. Example 1, Example 2.
Before you ask the question, first, specify a time period, and if possible an event. It is much easier to provide a comprehensive answer if you specify an event; we can research teh causes and effects of that event and discuss them intelligently. Second, doublecheck that the majority of the people accept all the assumptions. Sometimes this will cause me to eat crow; there are questions where the assumptions aren't obvious. But it is worth your while to take a moment to make sure that all the terms in your question are meaningful to the audience.
Can you evaluate the impact of Sujarkama's theory of mesonic exchange entitlements on the gross national product of the Jawethi province of Kronos under Reaganomics?
If you ask a question which relies on obscure details, without citing those details I will downvote you. If you ask a question that relies on obscure details and you cite those details, providing me the opportunity to learn something new, I will upvote you and cause fuzzy unicorns to bring you waffles.
The point of H:SE isn't to demonstrate your intellectual power & puissance; it is to get an answer to a question. If you can't be bothered to cite your sources, then there is a gravitational force drawing my mouse to the downvote button.
Someone once said that... ; is that true?
There are two problems with this question, and I'll wish for the ability to downvote twice.
First, cite your source. It makes a big difference if the "someone" who once said is a 3rd century monk, a member of the Nazi party in 1938, Paul Krugman, or Noam Chomsky. They all have different biases; they are reliable for different classes of fact. If you don't identify the source, then we're both playing darts in the dark, potentially in an open field.
The second problem is that this is very close to the example given in the FAQ of a question NOT to ask. "your question is just a rant in disguise: “__ sucks, am I right?”. If you're looking for people to confirm your opinion, H:SE is the wrong place.
If you want to learn, then do the basic research to enable scholarship. Tell us who said it, and then follow up with a question. "Disraeli said that ancient Greeks had no word for 'blue'; what color did they think the sky was?" Still tough to answer, but there is at least a starting point for research. (A good question would have cited Disraeli's claim.)