- Starting from Season 3, he changed from a nice person to a jerk who'd make fun of his friends.
- He makes fun of Harold a lot alongside Stinky in Harold's focus episodes, even to the point of fat-shaming him.
- His paranoia is now extremely grating and makes you feel annoyed instead of sympathetic.
- He's horrible in "Arnold Betrays Iggy", "Hey Harold!", "Weighing Harold", "Bag of Money", and "Harold vs. Patty."
- He and Stinky got no punishment for telling the school that Iggy wore bunny pajamas and getting Arnold humiliated.
- He was at his worst in "Bag of Money". When Arnold lost the money, he accuses him of stealing it, gets in his business about it, and even rallies the others to tie him up to a flag post. His apology when he found out that Arnold didn't steal does not help at all.
- In "Deconstructing Arnold", he stole Lorenzo's phone so he could prank call some people.
- Even after all he's done, his friends still hang out with him.
- In "Full Moon" Sid was never caught by Principal Wartz and nearly made Arnold face the consequences due to getting 4 weeks detention after Principal Wartz placed him under his threat of recieving a terrible black mark next to "FAILURE TO COOPERATE" on his permanent record. And Sid nearly got off the hook for what he and along with Harold and Stinky started which was the wrong thing to do. Which made Principal Wartz act even worse than Sid in a very rude negative manner.
- He's back to his old persona in Hey Arnold!: The Jungle Movie.
- Despite how he treats people, he's kind to Stinky, who's his best friend.
- At least he apologized for his actions in "Bag of Money".
- To be fair, Sid's actions in "Sid's Revenge" were justifiable, as he was blamed by Principal Wartz for a prank he didn't commit.
- He was much a better character from Season 1-2.
- He and Stinky got beat-up by Harold after the latter had quite enough of them teasing him in "Harold vs. Patty."