Application.Commandbars("Cell").Enabled = False
disables the menu completely. Be sure to enable it or the user will be
stuck with it this way.
Another option is just to disable it on a specific sheet:
Private Sub Worksheet_BeforeRightClick(ByVal Target As Range, Cancel As
Boolean)
Cancel = True
End Sub
This must be pasted into the sheet's module (right click sheet tab and click
View Code.
Or for an entire workbook:
Private Sub Workbook_SheetBeforeRightClick(ByVal Sh As Object, ByVal Target
As Range, Cancel As Boolean)
Cancel = True
End Sub
Pasted into the ThisWorkbook module.