OMG is just letters...
While sharing the Gospel with a lady, I asked her if she had ever used God's name in vein? She didn't understand what I meant so I clarified to her "... have you ever said 'oh my god' ?" to which she replied that she "only used the letters." So I helped her see her faulty logic by telling her that's like me telling her "F U" -- Her eyes got big and she realized that words, and letters, have meaning.