This event occurs when any part of a cell is clicked, including borders and padding. It also occurs when the user presses and releases the SPACE key while a button cell or check box cell has focus, and will occur twice for these cell types if the cell is clicked while pressing the SPACE key.
private void dataGridView1_CellClick(object sender,
DataGridViewCellEventArgs e)
{
if (dataGridView1.CurrentCell.ColumnIndex.Equals(3) && e.RowIndex != -1){
if (dataGridView1.CurrentCell != null && dataGridView1.CurrentCell.Value != null)
MessageBox.Show(dataGridView1.CurrentCell.Value.ToString());
}