Man I am trying to figure out which was the first R rated movie I saw in theater, but it's so tough. I am 100% sure I saw Alien 3 (1992) in theater. 100% sure I have not seen Aliens (1986) in theater. I am almost certain I saw Total Recall (1990) in theater, but again I am also pretty sure one of the first films I saw by myself in a theater was Lethal Weapon 3 (1992) so something is not quite right... or was it Lethal Weapon 2 (1989)? Man.... memories are all fucked up.
In the same line of thoughts, I am convinced the first movie I ever saw in theater was The Secret of NIMH (1982), but I also know for sure I saw with my school The Fox & The Hound (1981) in theater..... but that makes very little sense: I would have been in kindergarten in 81... so maybe the movie took a long while to reach Europe, or I saw a special screening or re-release.... who knows.... memories are all fucked up.