Not worst; first.
I don't know if others will find this thread interesting or not, but I thought I'd give it a try based on the popularity of the other thread about people's worst theater-going experience.
The very first movie I remember going to see was The Longest Day in 1962 when I was 6. My parent's dragged me along to the drive-in with them, I guess because there was a playground there as well.
http://cinematreasures.org/theaters/23892
The only thing I really remember from that night, was that I was bored out of my mind because half the movie was in German with English subtitles and I couldn't read yet (or at least not very well).
The first movies I remember going to on my own with a friend in a traditional movie theater were Viva Las Vegas in 1964, and Thunderball in 1965. I saw both of those at the Miracle Theater in Coral Gables, FL. (Which still exists, albeit as a playhouse now.)
http://cinematreasures.org/theaters/293