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. Compare this to the first film, where Angela is very shy and reserved but also sweet to the people who aren't bullying her, and is alongside other positive characters like Ricky and Paul.
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.
Michael might be even more hated than Alan. While the other campers had a justified reason to target Alan, he only tormented him For the Evulz and then skinned his pet frogs alive, which some people consider the only time Alan was sympathetic through out the story.
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.