Why do people expect you to believe crazy things they tell you?

Have you ever had someone tell you something completely outrageous and so unbelievable that what shocks you the most is the fact that they actually thought you would believe them? I'm an intelligent, educated person. The people I'm talking about are also intelligent, educated people. Do they actually believe that I am dumb enough to get sucked into their craziness?  It's such an insult to my intelligence when people tell me things that are so completely far from the truth. I say if you're not going to tell the truth, at least say something believable. Don't give yourself away by saying something ridiculous. Try it on yourself first. Would you believe you??