Sikh philosophy - Prohibited behavior (Wikipedia)

1. Non-logical behavior: Superstitions, or rituals which have no meaning, such as pilgrimages, fasting and bathing in rivers, gambling, worship of graves, idols or pictures, and compulsory wearing of the veil for women, are prohibited.
2. Material obsession: ("Maya") Accumulation of materials has no meaning in Sikhism. Wealth such as gold, portfolio, stocks, commodities, properties, et cetera, will all be left here on Earth when you depart. Do not get attached to them.
3. Sacrifice of creatures: Sati – Widows throwing themselves in the funeral pyre of their husbands, the act of slaughtering lambs and calves to celebrate holy occasions
4. Non-family oriented living: A Sikh is encouraged not to live as a recluse, beggar, monk, nun, celibate, or in any similar vein.
5. Worthless talk: Bragging, gossip and lying are not permitted.
6. Intoxication: The consumption of alcohol, drugs, tobacco, or other intoxicants is prohibited.
7. No priestly class: Sikhs do not have to depend on a priest for any of the functions that need to be performed.
8. Eating meat killed in a ritualistic manner (Kutha meat): Sikhs are strictly prohibited from eating meat killed in a ritualistic manner (such as halal or kosher, known as Kutha meat^[1] ), or any meat where langar is served.^[2] In some small Sikh Sects, i.e. Akhand Kirtani Jatha eating any meat is believed to be forbidden, but this is not a universally held belief.^[3] The meat eaten by Sikhs is known as Jhatka meat.
9. Having premarital or extramarital sexual relations^[4][5][6][7]

^{Source: http://en.wikipedia.org/wiki/Sikh_philosophy}