The film opens with the POV of the killer as she follows two councilors into the attic. Before proceeding with the murder, the camera pauses over some sleeping children, before moving on without harming them. This is foreshadowing the killer's identity as a grieving mother. It's likely looking at those kids reminded Pamela of what her son was like in life.
Given the killer's Freudian Excuse, this can apply to the reasoning behind most of the deaths.
Barry and Claudette are still on duty at the beginning, and they sneak off to fool around, leaving the kids. They're trusted with children's safety and they shirk that responsibility to have sex. And they also choose to do it nearby, risking the possibility that a child could walk in and see.
Ned is a sex fiend, who thinks of nothing but "kissing women", and is acting like more of a Jerkass than usual (according to Marcy). He also pretends to be drowning just so he can give Brenda an unwanted kiss, which is bound to be a sore spot for Pamela, considering her son actually drowned, and she was watching that scene.
Jack and Marcy have sex in one of the cabins that will be used by the campers. Pamela is bound to be furious at the idea of sex happening in a spot intended as a children's room (even if the intent is to stop Camp Crystal Lake from opening).
Brenda puts an adult spin on a traditional children's game - by getting Bill and Alice to play Strip Monopoly. Imagine Pamela's fury at the idea of turning an innocent family game into something sexual. Symbolically, Alice is the only one still fully clothed and she's the one to survive. But she was taking part in the game and about to take her blouse off, hence still being targeted by the killer.
Steve is implied to have had a relationship with one of his employees, and a much younger woman at that. And obviously, he's the one going to all the effort to re-open Camp Crystal Lake.
We see two counselors having sex in one of the cabins. Afterwards, we see the guy laying down, and an arrow is pushed through his neck from under the bed. OK, but then you realize, that means the killer was under the bed the entire time they were having sex! Eeeeeew.
That's Eeeeeew? You forgot about the corpse of one of the counselors on the bunk above the two counselors. Just as Eeeeew if you ask anyone.
