Bert pisses off the same rednecks he would later depend on to save his life, by stealing a candybar from them at the beginning.
Bert and Jeff make a bet to see who can last the longest drinking nothing but beer. Bert forgetting about this bet and drinking a sip of water ultimately killed him.
The first person Jeff and Bert find when they go looking for a phone so they can report that they had to incinerate the sick hermit, that person turns out to be the hermit's cousin.
Paul actually killed the girl he wanted to score with by urging her to drink some (tainted) water when she was upset.
When Paul walks in on Jeff and Marcy having sex, he advises them to practise "safe sex." He should've followed his own advice much later when he had sex with Marcy, because she had the same disease by the time they hooked up later on.
He actually tells Marcy he's concerned about not wearing a condom when they start screwing. But then he just takes her word for it when she tells him it's safe. It didn't work out too good for him in the end...
By the time she has sex with Paul, Marcy's infection has progressed far enough for his squeezing of her back to leave red welts. How squickky would it have been if they'd had sex only a couple hours later - like around the time she was shaving off her leg flesh - and her back started peeling off in his hands while she was still screwing him?
In Cabin Fever 2: Not that it matters to poor Paul at this point (because he's already dead), but how bone-chilling would it be if Paul had found out the only way to survive the disease was to amputate the body part that first contracted that disease? Remember, he actually got sick from a bareback sexual fling in the first movie.