Are you addicted to the Big Mac, or can you stop anytime you want?  Whatever your emotional issues with the burger, McDonald's is distancing itself from the mental-health parody ad which appeared on Boston's mass transit this month.   A McDonald's rep for the Boston area told Time the ad was not approved by the fast food company and that they asked it be taken down immediately.   The ad showed a female looking distraught.  It said "You're Not Alone.  Millions of people love the Big Mac."   At the bottom of the ad it said "Call (followed by the McDonald's corporate 800 number).  The ad was designed by the Boston advertising rep for McDonald's.