Oh I don't know about that. Some of the nicest people I know are not Christians. And some of the nastiest people I know are.
I too know people who would not profess to being Christians, who clearly demonstrate Christ's commandment to "love one another" by their unselfish acts of kindness to those in need. Conversely, some Christians I know act in ways that are not very Christ-like. Bottom line: we humans aren't perfect and we're all capable of doing both nice and nasty things. But Jesus Christ is perfect love and when we allow Him to direct our lives, then we'll be living as he intended us to--out of love for our fellow human beings. And how do we do this? According to that great humanitarian, the "Saint of the Gutter," Mother Teresa--who lived her life in the service of the poorest of the poor, the weakest of the weak--we do this through prayer. She said, "And do you think if I didn't pray I would be able to love the poor? It's Jesus that puts love in my heart when I pray." (Excerpted from homily by Cardinal Comastri; see http://www.catholicnewsagency.com/news/cardinal-comastri-recounts-how-mother-teresa-saved-his-priesthood/ )
Ginny, you may want to read chapter 10 in C.S. Lewis's book Mere Christianity called 'Nice people or new men'. He disucsses this point you make. He begins the chapter with this question: "If Christianity is true why are not all Christians obviously nicer than non-Christians?"