Re: This was actually genius..
As long as BK act contrite, I suspect that the number of people in BK's target market that approved of the tongue in cheek remarks would have been close to 100%. And as for market share, in a mature, stable market, altering it by a few percentage points for a month or two is the best you can hope for.
Just because Twitter complains about something doesn't mean the complainers make any real difference.
Similarly people who complain to the ASA - having your complaint upheld doesn't mean the message hasn't already got across and been approved by the audience, regardless of the outcome.