why do people come on yahoo and ask stupid questions?

Because they think it's funny, or they just want tons of answers.

I have seen many questions like How do I ask a question? I just think thats a waste of points, rude questions can be from trolls.

A "troll" is someone who intentionally and persistently posts inflammatory messages about sensitive topics to bait users into responding or provoke a confrontation. We also consider people to be trolls when they persistently misuse product features such as the ratings system to negatively target others.

stupid is desperate by the reader of the question. What i think of is stupid does no longer be to somebody else and a lot of cases it quite is an soliciting for an opinion. I delight in the final public of questions and solutions.

like this one? clearly people are bored and need to go do something

because they have no lives and r bored

Because they think they're cool and they're not, they're just trolls.