Darkness-Induced Audience Apathy: The only thing you could really say in Alan's defense is that his tormentors can be just as bad as him, if not worse (especially Michael). The only person who comes close to being a decent human being is the lifeguard.
Take That, Scrappy!: That said, he sure goes through a lot of punishment throughout the film, and ultimately gets beaten senseless by his older brother.
Unintentionally Unsympathetic: Alan. He's a whiny, mean fat kid who regularly bullies the younger campers, yet the audience is supposed to feel sorry for him when he gets bullied or complains that he doesn't have any friends. Most of his negative treatment is arguably a reaction to him being an asshole to other people. Angela claims she was protecting him but it's clear he's exactly like (and in some cases worse) than the victims she targets.
The Untwist: It's obvious the "sheriff" is really a woman and Angela. The voice box disguising "his" voice makes it even more obvious.
What an Idiot: T.C. and Spaz in the spear sequence. Sure, let's keep looking down the hole someone just shoved a pointy stick through. What happens next is unsurprising.