There is no reason to feel hurt. The girl likes you enough that she is safe guarding you from any potentially bad social experience with her friends. Sometimes controlling your laughter at an odd behavior you have never seen can be humurous. I have myself laughed at a weird stutter of a friend, and of my own. It's natural. Your girl might also be taking extra caution as she knows her friend could potentially laugh at you. TV shows and movies haven't made our lives easier, so people think it might be a joke or it's okay to laugh, and she is protecting you. I think that's a very kind gesture and you should be thankful to have someone so thoughtful in your life.