The default format string for System.DateTime is "G" as in System.DateTime.ToString("G") where G is one of the presets. from source
Edit 1:
Globalization.CultureInfo customCulture = new Globalization.CultureInfo("en-US");
customCulture.DateTimeFormat.ShortDatePattern = "yyyy/M/d";
System.Threading.Thread.CurrentThread.CurrentCulture = customCulture;
System.Threading.Thread.CurrentThread.CurrentUICulture = customCulture;
DateTime dt = Convert.ToDateTime(DateTime.Now.ToString("M/d/yyyy"));
Console.WriteLine(dt.ToString())