C#

namespace mouseclick
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            listBox1.MouseClick += new MouseEventHandler(listBox1_MouseClick);
            listBox1.Items.Add("aaaaaaaaaaaa");
            listBox1.Items.Add("aaaaaaaaaaaa");
            listBox1.Items.Add("aaaaaaaaaaaa");
        }

        void listBox1_MouseClick(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                MessageBox.Show("Left Button"); // Works
            }
            if (e.Button == MouseButtons.Right)
            {
                MessageBox.Show("Right Button"); // Does not work  
            }
        }  
    }
}