I've always been citing this verse in Matthew. In context it is from Jesus' sermon on the mount. He is talking to the people and the hyprocritical ways of being self-righteous and pointing flaws in others without looking at one's self first.
For me I've always cited: "I'm too busy lumberjacking the forest in my own eye to worry about the speck in my brother's." How about you? What logs, specks, forests are you working on?