Two Irishmen were working on the roof of a building one day when one made a mis-step and fell to the ground; the other leaned over and called: "Are ye dead or alive, Mike?"
I'm alive, said Mike, feebly.
Sure, yer such a liar I don't know whether to believe ye or not.
Well, then, I must be dead, said Mike, "for ye would never dare to call me a liar if I were alive."