I saw The Ring in theaters, but my homies and I smoked a blunt, and I was gone. I think I was 17. I was smoking a lot and movies were fun, but I was often so high, I was just befuddled. Same thing in Abandon. I was barely able to follow, even the threadbare plot of The Ring, but it was fun, I am sure I jumped too.
Also, saw The Blair Witch in theaters, which was a great experience, but not really a terrifying movie, but summer, horror movies in the mall with your friends, it didn't get much better.
Paranormal was a fun one too, saw by myself, but Insidious, also by myself, in an empty theater on a weeknight, was pretty intense, as I remember. The funniest part was when it ended, and that music started playing, I kind of ran out of the theater all fast through that little dark hall between the theater and the exit, and burst out, looking a little crazy. Perfect way to enjoy a scary movie.
Strangers wasn't quite as intense to me, as others felt it was, but it was fun. Saw in theaters.
What Lies Beneath, I saw alone in theaters when I was 14, and I kind of ran home, got lost, and spent half the night closing the door to my bathroom, and playing RR. Vol. 2.
Seeing scary movies alone is a great experience, for the horror fan.