Tell him to find out what it is her mom doesn't like about him from other family members. If it is attitude smile and be pleasant. Is it wild hair and clothing ? Tone down. He could tell the mom outright that he understands her concern for her daughter. Don't sneak around or her mom will really get ticked off. Spend some time at that house if possible (even with a brother) and let her mom see that he is ok. If he gets to go out with her obey to the T whatever rules are set down. After awhile her mom will loosen up considerably. If all this fails chalk it up to experience and move on. Auntie