public partial class Form1 : Form
 {
  ContextMenuStrip MyContextMenuStrip = new ContextMenuStrip();
  bool CloseClicked = false;

  public Form1()
  {
   InitializeComponent();

   // add close item, name it
   MyContextMenuStrip.Items.Add("Close");

   // add separator
   MyContextMenuStrip.Items.Add("-");

   // handle MouseDown to no reshow context menu strip
   this.MouseDown += new MouseEventHandler(Form1_MouseDown);

   // we will add items here
   MyContextMenuStrip.Opening += new CancelEventHandler(cms_Opening);

   // we will control closing here
   MyContextMenuStrip.Closing += new ToolStripDropDownClosingEventHandler(cms_Closing);

   // we will stash a flag on what item is clicked here
   MyContextMenuStrip.ItemClicked += new ToolStripItemClickedEventHandler(cms_ItemClicked);

  }

  void cms_ItemClicked(object sender, ToolStripItemClickedEventArgs e)
  {
   if (e.ClickedItem.Text == "Close")
   {
    CloseClicked = true;
   }
  }

  void cms_Opening(object sender, CancelEventArgs e)
  {

   // The opening event is automatically cancelled if there are no items to display. 
   // To dynamically populate a dropdown in the Opening event, make sure to set 
   // e.Cancel = false. In this case, we always have an item.
   //
   // Add a timestamped item
   MyContextMenuStrip.Items.Add(DateTime.Now.ToString());

   // reset flag
   CloseClicked = false;
  }

  void cms_Closing(object sender, ToolStripDropDownClosingEventArgs e)
  {
   e.Cancel = true;

   // only close if the close item is chosen
   if (e.CloseReason == ToolStripDropDownCloseReason.ItemClicked && CloseClicked)
   {
    e.Cancel = false;
   }
  }

  private void Form1_MouseDown(object sender, MouseEventArgs e)
  {
   // show on right click
   if (e.Button == MouseButtons.Right)
   {
    // only if not already showing
    if (!MyContextMenuStrip.Visible)
    {
     // coordinates relative to form
     MyContextMenuStrip.Show(this, e.Location);
    }
   }
  }

 }