private Point rtfLocation;

    private void textBox1_MouseDown(object sender, MouseEventArgs e)
    {
        if (MouseButtons == MouseButtons.Right)
        {
            rtfLocation = this.PointToClient(textBox1.PointToScreen(new Point(e.X, e.Y)));
            textBox1.ShortcutsEnabled = false;
            richTextBox1.Location = rtfLocation;
            richTextBox1.Show();
        }
    }

    private void richTextBox1_MouseDoubleClick(object sender, MouseEventArgs e)
    {
        richTextBox1.Hide();
    }

    private void richTextBox1_Leave(object sender, EventArgs e)
    {
        richTextBox1.Hide();
    }

    private void Form1_Click(object sender, EventArgs e)
    {
        if (richTextBox1.Visible)
        {
            richTextBox1.Hide();
        }
    }

    private void textBox1_Click(object sender, EventArgs e)
    {
        if (richTextBox1.Visible) richTextBox1.Hide();
    }

    private void richTextBox1_VisibleChanged(object sender, EventArgs e)
    {
        textBox1.ShortcutsEnabled = ! richTextBox1.Visible;
    }