Phrase made famous by the 1972 child molestation scandal of Jackson, Mississippi. 'Nasty Jack' Flynn, the 13 time repeat offender and part time civil war re-enactor, though appalling was made especially famous for his unique habit of screaming 'I'm in like Flynn' in a constipated voice as he would sodomize his victims. The phrase is not as well known in most parts of the country, but is still prevalent in the 'Deep South' of the United States of America to describe feelings of determination and/or conviction.
In the original Tron movie, Kevin Flynn, a talented computer programmer, was transported to the Game Grid by an experimental laser in development by ENCOM, the company that fired Flynn and stole his code.
The phrase In Like Flynn can be a reference to Tron and means having access to or completing your goal.