Forget everything else you know and remember this one thing. If the whole world followed suite all the bullshit would simply cease. This of course is what every religion in the world aims for, to instill this one simple value to the fullest while we forget the basics and then kill each other over the details.

Baha'i Faith Lay not on any soul a load that you would not wish to be laid upon you, and desire not for anyone the things you would not desire for yourself.
Ascribe not to any soul that which thou wouldst not have ascribed to thee, and say not that which thou doest not. Blessed is he who preferreth his brother before himself. (Baha'u'llah, Gleanings, LXVI:8 )

Brahmanism This is the sum of duty: do naught unto others which would cause you pain if done to you. (Mahabharata 5:1517)

Buddhism Hurt not others in ways that your yourself would find hurtful. (Udana-Varga 5.18)
A state that is not pleasing or delightful to me, how could I inflict that upon another? (Samyutta Nikaya v. 353)

Christianity Do unto others as you would have them do unto you. (Matthew 7:12)
...and do not do what you hate... (Gospel of Thomas 6)

Confucianism "Surely it is the maxim of loving-kindness: Do not do to others what you would not have them do to you." (Analects 15:23)
Tse-kung asked, 'Is there one word that can serve as a principle of conduct for life?' Confucius replied, 'It is the word 'shu' -- reciprocity. Do not impose on others what you yourself do not desire.' (Doctrine of the Mean 13.3)

Hinduism Do not do to others what would cause pain if done to you. (Mahabharata 5.1517)
One should not behave towards others in a way which is disagreeable to oneself. (Mencius Vii.A.4)

Islam Not one of you is a believer until you wish for others what you wish for yourself. (Fourth Hadith of an-Nawawi 13)
No one of you is a believer until he desires for his brother that which he desires for himself. (Sunnah)

Jainism One should treat all creatures in the world as one would like to be treated. (Mahavira, Sutrakritamga)
Therefore, neither does he [, a sage,] cause violence to others nor does he make others do so. (Acarangasutra 5.101-2)
In happiness and suffering, in joy and grief, we should regard all creatures as we regard our own self. (Lord Mahavira, 24th Tirthankara)

Judaism What is hateful to you, do not do to your neighbor. (Talmud, Shabbat 31a; Tobit 4:15)
...thou shalt love thy neighbor as thyself. (Leviticus 19:18)

Native American Spirituality Humankind has not woven the web of life. We are but one thread within it. Whatever we do to the web, we do to ourselves. (Chief Seattle)
Respect for all life is the foundation. (The Great Law of Peace)

Paganism (Roman) The law imprinted on the hearts of all men is to love the members of society as themselves.

Scientology "Try not to do things to others that you would not like them to do to you."
"Try to treat others as you would want them to treat you." (The Way to Happiness by L. Ron Hubbard)

Shintoism Hurt not others with that which pains yourself. (Udana-Varga 5.18)
The heart of the person before you is a mirror. See there your own form.

Sikhism Don't create enmity with anyone as God is within everyone. (Guru Granth Sahib, pg. 1299; Guru Arjan Devji 259)
Compassion-mercy and religion are the support of the entire world. (Guru Japji Sahib)

Sufism The basis of Sufism is consideration of the hearts and feelings of others. If you haven't the will to gladden someone's heart, then at least beware lest you hurt someone's heart, for on our path, no sin exists but this. (Dr. Javad Nurbakhsh, Master of the Nimatullahi Sufi Order)

Taoism Regard your neighbor's gain as your own gain and regard your neighbor's loss as your own loss. (Tai Shang kan Ying P'ien, 213 - 218)
I am good to the man who is good to me, likewise, I am also good to the bad man. (Tao Te Ching)

Unitarianism We affirm and promote respect for the interdependent web of all existence of which we are a part. (Unitarian principle)

Wicca A'in it harm no one, do what thou wilt (i.e., do whatever you want to, as long as it harms nobody, including yourself). (The Wiccan Rede)

Yoruba (Nigeria) One going to take a pointed stick to pinch a baby bird should first try it on himself to feel how it hurts.

Zoroastrianism Do not do unto others whatever is injurious to yourself. (Shayast-na-Shayast, 13.29)
That nature alone is good which refrains from doing unto another whatsoever is not good for itself. (Dadistan-i-dinik 94:5)