C# date formatting is losing slash separators

Console.WriteLine(DateTime.Now.ToString("ddd M/dd/yy", CultureInfo.InvariantCulture));
            Console.ReadLine();

try the above

You could also use

Console.WriteLine(dateTime.ToString("ddd M'/'dd'/'yy"));

That's a possible solution if you're not using the invariant culture as mentioned in other answers here.

The default behavior of the "/" (slash) in a format argument is to use the current's culture date separator.

To force the "/" (slash), you must precede it with a "\" (backslash).

Ex.: "yyyy\\/MM\\/dd" will always display a date like "2015/07/02" independent of the current culture in use.