var message = "今天天气正好[哈哈]，可惜明天要下雨。[鄙视]";

//方案一：效率低（多次遍历），但是简单易懂

string[] emotions = { "[哈哈]", "[调皮]" };

string cleanMessage = message;
foreach (var emotion in emotions)
{
       cleanMessage = cleanMessage.Replace(emotion, string.Empty);
}

//方案二：只遍历一次message

string[] emotions = { "哈哈", "调皮" };  //注意跟上面不同

var cleanMessage = new StringBuilder();
int position = 0;
while (position < message.Length)
{
      if (message[position] == '[')
      {
            var part = message.Skip(position + 1).TakeWhile(c => c != ']').ToArray();
            if (emotions.Any(e => e.SequenceEqual(part)))
            {
                  position += part.Length + 2;
                  continue;
            }
       }

        cleanMessage.Append(message[position]);
        position++;
}