The Coexist bumper sticker has received much criticism for its anti-Christian intentions, but ironically, when used correctly, coexistence is a natural Christian message.
As is frequently pointed out to the more intolerant believers in Left Wing politics, it is entirely possible to disagree with someone without hating them. If you're gay, I can disagree with you without hating you. If you're a Muslim, I can disagree with you without hating you. If you're a Mormon, I can disagree with you without hating you. If you're an Evolutionist, a Buddhist, a Hindu, I don't care what you believe, or how you live, I can disagree with you without hating you. Not only can I, but I must.
Coexistence isn't just an option in Christianity, but a command. It is not a creative suggestion, but a requirement. It is not guidance that may lead to prosperity, but a law, the breaking of which can only be covered by the blood of Jesus. It is not exclusive, either. Paul didn't tell the Roman Christians to live peaceably with some men, or even with most men, but, as far as it depended on them, to live peaceably with all men. In other words, the only time when it is excusable to not coexist is when you are not the deciding factor. If strife is unavoidable, then we have an excuse, but so far as we can live at peace, we must.
Therefore, although the Coexist bumper sticker seems to have been created as a club to beat Christians round the head with, I suggest we take it captive in obedience to Christ (2 Corinthians 10:5). Use it as an opportunity to spread the Gospel, so that men may not only coexist with each other, but with God.