I haven't slept well lastnight (only 4 hours) so please bear with me... but what is the joke on this snippet?

"I Don’t Know".ToJson();

    public string ToJson()
    {
        var s = new StringBuilder("{");
        for (var i = 0; i < CustomField.CustomFieldOption.Count; i++)
        {
            var item = CustomField.CustomFieldOption[i];
            s.Append("\"" + item.CustomFieldOptionId + "\"");
            s.Append(":\"" + item.OptionName + "\"");
            if (i < CustomField.CustomFieldOption.Count - 1)
            {
                s.Append(",");
            }
        }
        s.Append("}");
        return s.ToString();
    }