Do you know where you were on this day 18 years ago?You probably don't, but I remember it like it was yesterday. I was at a movie theater formerly known as Ridge Cinema in Davie, Florida, watching "The Dark Knight" on opening day with a group of my closest friends.I can recall this partially because of how mind-blowing the movie was (more on that in a bit) but also because some guy had a heart attack in the front row and I had to run to the conc…