Via Mind Hacks, a brief tour of cultural sex taboos:
The Cuna of Panama approve of sexual relations only at night in accordance with the laws of God. The Semang of Malaysia believe that sex during the day will cause thunderstorms and deadly lightning, leading to drowning of not only the offending couple but also of other innocent people. And the West African Bambara believe that a couple who engage in sex during the day will have an albino child.
Sometimes, sex is prohibited in certain places. The Mende of West Africa forbid sexual intercourse in the bush, while the Semang condemn sex with camp boundaries for fear that the supernatural will become angry. Among the Bambara, engaging in sexual relations out of doors will lead to the failure of crops.
Sex taboos can also apply to certain activities. Often, sex prohibitions are associated with war or economic pursuit. The Ganda of Uganda forbid sexual intercourse the night before battle.