When a policeman shows up at the camp looking for Crazy Ralph, it is badly timed to Ned running out of the cabin dressed as an Indian, screaming and dancing around. He says "oh shit" when he spots the cop but the characters don't bat an eyelid. It adds nothing to the plot and is just so random.
There's a conversation between Jack and Marcy that has nothing to do with anything really and has no impact on the plot. Just before going into the bunks to do it, they have a talk by the lake. Marcy tells Jack about a dream she frequently has where it's raining and the rain turns to blood.
Right before she's killed, Marcy is in the outhouse and randomly looks into the mirror to do a Katherine Hepburn impression, quoting The Rainmaker.
Critical Dissonance: Critics more or less hated it, but it went on to be one of the biggest slasher films ever made.
It Was His Sled: The killer is probably known to most people who are familiar with the series. Though to those unfamiliar with the series, they still might be surprised to see Jason's lack of appearance.
Jerkass Woobie: Pamela Voorhees. The novelization implies she only went on a killing spree to save further campers from Jason's fate.
Narm Charm: Mrs. Voorhees alternating her voice between her own and "Jason's".
Tear Jerker:The villain isn't Jason, but rather his mother, who went completely insane after the supposed "death" of her son. And then the sequels reveal he was never dead to begin with, meaning her horrible deeds accomplished nothing— except to inspire an innocent child to become a violent killer.
Unbuilt Trope: Alice is the film's Final Girl yet you'd be surprised that she's a) implied to be having an affair with Steve, b) provides Fanservice in the form of a bikini, c) happily smokes and drinks with the others, and d) is about to strip during the Strip Monopoly game (but gets stopped when the door blows open). She's also blonde and one of the few Final Girls to be blonde.