When some unbelievers get saved they are excited. They're pumped. All they can think about is Jesus and all they feel is peace and gratitude.
They don't know the rules yet, so they start listening to Christian radio and reading Christian books and putting Jesus fish on their cars and wearing WWJD bracelets and talking to people about Jesus and treating other Christians like close friends. They're suddenly self-conscious about their language, whether they're cussing or not. They think about things like if it's okay to drink or watch R-rated movies.
And they don't do any of those things out of legalism or brainless conformity or selling out to Christian consumerism but simply because they're just so freaking excited about being a Christian that it consumes their thinking and acting and they're just energized by Jesusy thoughts and Jesusy language and flat-out being Jesusy.
Then a Christian who knows the rules gets ahold of them and out of embarrassment does his best to make the new believer less Jesusy and more cool, more presentable, less dorky.
Because these three remain in contemporary evangelicalism: aloofness, selfishness, and coolness, but the greatest of these is coolness.