C#

private System.Windows.Forms.ContextMenu emptymenu = new ContextMenu();
private System.Windows.Forms.ContextMenu oldmenu;
private void button1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
    if(e.Button == MouseButtons.Right)
    {
        if(button1.ContextMenu!=emptymenu)
            oldmenu = button1.ContextMenu;  //this will save the original menu.

        button1.ContextMenu = emptymenu; //this setts a empty menu to the property, which has the effect that no menu is shown.
    }
    else if(e.Button == MouseButtons.Left)
    {
        if(oldmenu!=null)   //the right mouse button was already pressed
        {
            button1.ContextMenu = oldmenu;
        }
        button1.ContextMenu.Show(button1, new Point(e.X,e.Y));
    }
}

private void button1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
    if(e.Button == MouseButtons.Left)
    {
        if(button1.ContextMenu!=null)
        {
            button1.ContextMenu.Show(button1, button1.Location);
        }
    }
}

private void button1_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
    if(e.Button == MouseButtons.Left)
    {
        if(button1.ContextMenu!=null)
        {
            button1.ContextMenu.Show(button1, new System.Drawing.Point(e.X, e.Y));
        }
    }
}

button1.ContextMenu.Show(button1, Cursor.Current.Position);

Stefan Troschtz wrote:

button1.ContextMenu.Show(button1, Cursor.Current.Position);

Martin# wrote:

I assume that this was out of your head without testing

Martin# wrote:

But this is also not the right solution because the position of the contextmenu is relative to the button location. So you would have an offset depending on the position of the form.

Martin# wrote:

I think only the eventarg members X and Y are giving the right location, without an additional calculation of offsets.

Stefan Troschtz wrote:

Overall, a quite lousy post of mine