Pet peeve: I'm at a party and I just poured myself a yummy beverage.  I get chatting.  I want to take a sip of my yummy beverage.  I look.  It's in the midst of a whole bunch of other random yummy beverages.  All is lost!  I'm not about to take a chance during cold and flu season.

Avoid this terrible party faux pas by making it obvious and fun for your guests to label their cups.