None of these event handlers will actually run. Not the form's OnMouseClick() method since you are not actually right-clicking the form. And not the tab page's MouseClick event handler since you gave the TabControl a context menu. So lastpoint being empty is the expected outcome.
It is not clear how you want this context menu to work. If you use it by right-clicking the tab page then it is simple, just destroy the selected page:
private void closeToolStripMenuItem_Click(object sender, EventArgs e) {
tabControl1.SelectedTab.Dispose();
}
If you activate it by right-clicking a tab, one that isn't selected, then it gets more complicated. You have to memorize which tab was clicked on, do so by using the context menu's Opening event:
private TabPage RightClickedTab;
private void contextMenuStrip1_Opening(object sender, CancelEventArgs e) {
RightClickedTab = tabControl1.SelectedTab;
var pos = tabControl1.PointToClient(Cursor.Position);
for (int tab = 0; tab < tabControl1.TabCount; ++tab) {
if (tabControl1.GetTabRect(tab).Contains(pos)) {
RightClickedTab = tabControl1.TabPages[tab];
break;
}
}
}
private void closeToolStripMenuItem_Click(object sender, EventArgs e) {
if (RightClickedTab != null) RightClickedTab.Dispose();
}