How do you globally set the date format in ASP.NET?

You can change the current thread culture in your Global.asax file, and override the date format for example:

using System.Globalization;
using System.Threading;

//...
protected void Application_BeginRequest(Object sender, EventArgs e)
{    
  CultureInfo newCulture = (CultureInfo) System.Threading.Thread.CurrentThread.CurrentCulture.Clone();
  newCulture.DateTimeFormat.ShortDatePattern = "dd-MMM-yyyy";
  newCulture.DateTimeFormat.DateSeparator = "-";
  Thread.CurrentThread.CurrentCulture = newCulture;
}