The Irishman-drinking-three-Guinnesses joke reminded me of this chestnut, which I heard many years ago: Two businessmen who live in suburban Connecticut and work in New York City decide to get themselves a mistress. They set her up in her own apartment in the city, and agree to split 50-50 all expenses related to her. A few days every week, one of the men calls his wife to say he'll be working late and will take the late train home, and then wines and dines the mistress all evening. The men alternate evenings with her, and things go fine for several months. One day the mistress announces to the two men that she is pregnant. They decide to do the right thing: they tell her that they will take care of the baby financially, splitting all expenses 50-50. Nine months later the mistress goes into labor on a day that one of the men is out of town on a business trip. The other man accompanies her to the hospital. When the absent businessman returns, he heads directly for the hospital, and finds his friend looking very glum outside the maternity ward. "Is she alright? Were there problems with the birth?", he asks his friend. "Oh, she's fine," replies the first man. "But I'm afraid I have some bad news. She had twins, and mine died."
(From the "Rest" of RHF)