why do people ask fake questions on yahoo answers?

The name for users who do this in most cases is 'Troll', Internet trolls are users of a site who deliberately post questions and answers which they know is a sensitive issue which will cause annoyance and possibly a confrontation on the site, these users thrive on people acting negatively towards them.

That's a good question. I think some people are sicker than others! It like why do some people destroy property or lie for the sake of lying or send virus's etc... they are immature, bored and idiots!