"Lie Detector Chair." joke
This professor of psychology at Harvard built a truth-telling chair. Every time someone sitting it lied, the bottom of the chair - essentially a trapdoor mechanism - collapsed sending the seated person flying to the ground. He knew it worked - he'd tried it. But he had to do some research before any one would believe him.
So he advertised in the USA Today for volunteers to come along and they'd get a fiver for their troubles, every hour. He received loads of replies and as such was able to take from any selection he liked. As a control for the experiment he decided to pick basketball fans, and invited three along for the first day of trials.
Anyway, the first day came and a Denver Nuggets fan arrived, he sat in the chair and began to speak. "I think the Nuggets are definitely a force to be reckoned with in the West..." and instantly the chair collapsed, sending him sprawling to the floor before he could carry on.
Next, an Orlando Magic fan arrived, he sat in the chair and began to speak... "I think the Magic are still capable of mounting a similar challenge on the title as last season" and instantly the chair collapsed, sending him sprawling to the floor before he could carry on.
Then a Golden State fan arrived, he sat in the chair and began to speak... "I think..." and instantly the chair collapsed sending him sprawling to the floor.
Not enough votes...