Johnathan Frost
He's earliest memories of the boarding house include his grandparents, Ernie, Mr. Hyunh, the Kokoshka's and Johnathan Frost. As a young boy he's missing his father's strong arms and his mother's hugs and spends most of his time with Ernie when not with his grandparents. Despite this he can't help but notice that Mr. Frost is starting to smell funny and come in and out at all hours. When he notices him collapsing to the ground, his kind nature compels him to check on him and the last he sees is blood-shot red eyes before he's hit and it hurts.
He can hear Ernie and Mr. Hyunh roaring and tackling Mr. Frost as that man tries to get up and he just doesn't understand. Everything hurts and he wants to parents to make everything feel better. His mother to hold and sing to him, his father to be his strong rock but their not there and so he runs to grandparents with tears in his eyes and then his grandfather is roaring and Mr. Frost is never seen at the boarding house again.
It's not until he's older than he understands that Mr. Frost fell into the bottle after losing his job. Underneath the fear he holds there is a bit of pity, but Arnold will never forgive the man who hit him when he was three.
Lana Vail
She wasn't there long about two years, but there is something about her that makes him uneasy. It creeps on him when she asks him to for help with chores. It creeps on him with the way there is an undercut of something in her words and with the way she looks at him.
When she moves, he feels relieved and despite her apologizing to him (he doesn't understand why she looks so self-disgusting as she does so, and in all honesty he's afraid too), he's never able to forgive her for making him feel so unclean.
Iggy
In all honesty his issues with Iggy mainly involve his own issues with himself. When he looks back at it, despite the anger at Iggy (him not listening, the humiliation at wearing bunny pajamas) there is a deeper horrification at himself.
Just how did he forget all common sense and point out Sid and Stinky were behind it? Was he that desperate to liked, to be respected, was he that horrified at having someone believe he hurt them on purpose, that distraught over someone being mad at him that he put himself through such humiliation?
When he reflects on it Arnold just so feels so disgusted at how he acted that he barely gives Iggy any thought. So he's never able to even contemplative possibility of forgiving Iggy because every time he thinks of those events he becomes ill and can't forgive himself.
Even if he could forgive himself for how he acted, he doubts he could ever forgive Iggy for being so unreasonable.
Big Bob Pataki
For a second he can't breathe when he hears it and there's such a rush of anger and sadness rushing through him. What kind of man, what person, what parent, would so cruelly call him an orphan? Doesn't that man understand what's saying? Doesn't he understand that every time he calls him an orphan that he's saying his parents are...? No, Arnold can't ever bring himself to ever think the word. They are out there, they will come back they have too!
He's never able to forgive Big Bob for what he insinuates with his thoughtless cruel comments.
Alphonse Perrier du von Scheck
Scheck tried to destroy his home, separate him from his friends, and tear apart his family! His friends are one of the most important things to him and the thought of being forcibly separated from them scares him. The thought of never seeing Gerald, someone he views as a brother, hurts. The thought of never seeing other boarders who have become family, is agonizing, but most importantly of all what about his parents?! His parents will come back someday, they have too, and how could they find him if the boarding house isn't there?!
No, he will never be able to forgive Scheck and when he thinks about it, might even hate him.
Author's Note: La Sombra was going to be included but he was being difficult and I couldn't decided on the exact fate of Arnold's parents.
Johnathan Frost is an OC and the Lana section is a reference to how the creators wanted her to have a crush on Arnold and him being uncomfortable with it.