Etiquette is a must-add to your business skills portfolio, especially at office holiday party time.  If you feel a bit stressed by your less-than-formal comportment, take heart.  With a few tips, you can shine at your company gala without becoming tomorrow’s water-cooler entertainment! Job One:  Attend!   Yes, many corporate functions can be tedious, but there are upsides to appearing.  First, read the invitation and …