任何现有的字典>其中的值集合不能包含键

我需要以下内容（为简洁起见，此处使用字符串作为类型）：

MyDictionary : IDictionary<string, List<string>>
{
    private readonly Dictionary<string, List<string>> _collection;
    ...
    // The collection cannot contain the key
    public void Add(string key, List<string> value)
    {
        _collection.Add(key, new List<string>(value.RemoveAll(p => p == key));
    }
}

因此，在使用中，您可能有：

string myName = "Superstringcheese";
List<string> myFriends = new List<string> {"John", "Jane", "Jerry"};
string yourName = "Someone";
List<string> yourFriends = new List<string> {"John", "Bill", "Ted"};
var myDic = new MyDictionary();
// It's okay that each of us (each key) has some friends that are the same. It's not okay for me to have myself as a friend. The add method would check if the key is contained by the value collection and remove it if necessary.
myDic.Add(myName, myFriends);
myDic.Add(yourName, yourFriends);

在我重新发明任何轮子之前，是否有执行此操作的本机集合类型，或者有人知道流行的实现吗？