This is actually a really interesting topic because Soleum rlly seems to be lacking in the anger department. Its to the point where it doesn't seem to be the case where Soleums just not an angry person. Instead its been theorized that this is (for some reason) a filter of The Good Friend.
As far as I'm aware and remember Soleum has gotten mad 7 times and only two are definitely of them seem to be of his own accord while two others are miscellaneous.
Now when I say mad I mean yelling, anger, rage. Getting upset, distressed, or annoyed does not count. I'm also not counting small occasions due to contamination (such as his anger when seeing the intruders as a Sekwang high schooler). I'm only counting big moments which resulted in something happening.
He gets mad 2 times due to contamination. Once in Part 1 as The Golden Flower Mascot where he gets upset at Magic Bunny's for attempting to ruin his ceremony and he nearly kills the contaminated guests. And another time in Part 2 when he gets a temp tatoo that makes him hurt Kwak Jekang. Both times once its over he snaps out of it pretty quickly and is immiedatly aware and guilty.
Now he gets mad 3 times as 130666 and one may not be of his own accord. He gets mad as he crushes the bathroom spirit, infuriated and enraged at his crushed mind and body and taking it out on the spirit. The other time is when Cheong grabs him by the head like an animal and he feels a genuine rage. This one is rlly unusual cause Braun even commented on it. Its also the only time Soleum has explicitly told us he's angry.
The Third time is unusual. While 130666 usually has a silent giant rage that looms, this one doesn't seen to match it all. It was when j3 tried to devour Soleum and he had the thought process of being aggravated and offended such a thing would try to devour him. In a superior tone. He immiedatly gets confused as that wasn't him. My guess it was Yongyong's thoughts because the body was closer to hers than his at this point?
Anyways now we get to rlly interesting bits. The times that aren't influenced by Contamination or your mind and body being a crushed mess. Instead this is purely Soleum. Influenced by nothing but his own mind.
And this rlly makes the audience see how strange his anger is. How it happens at such unusual times. Because he never ever gets angry. Except for these two times with quite a large similarity.
They both relate to him going home. Or how he got here from home. They relate to his position here.
The first time was when he met a researcher from Cheerful and it was revealed how he was summoned here. It was revealed he was the reason for Sekwang city. And he got mad. A genuine cruel anger. He made the researcher figure out his identity as the one from a world without ghost stories and told him that he would never help him. He left the researcher to die knowing that cruel bit of information. Brushed it out of his mind and moved on.
This moment of anger rlly rlly stands out because it doesnt feel like Soleum at all. Soleum is kind and always feels an instinctual feeling to help people. And it was just shown that Cheerful genuinely had good intentions and no plan to harm anyone. They just wanted to create a safe world.
And Soleum crushes those dreams. Didnt even give them a second thought and basically spat in this man's face. And thats so weird! Because that doesnt feel like Soleum at all!
The next time Soleum gets mad is at Agent Choi. When Choi tells him that he can't go home. Soleum tries to calm himself down, to analyze the situation and figure a way out. Like he always does. But he fails. His anger blows up and all planning goes out the window. He yells, he nearly grabs Choi, he's angry, and he runs.
This doesn't make sense at all until the theory that I stated above comes up. That Soleum IS angry. This is just the filter stopping him from being.
Because the OG Soleum. IS angry. IS selfish. He angrily declares and says that this entire city can solve its own problems. Most of the entire interaction with him was filled with his angry and desperate thoughts. So unlike the Soleum we know who's nearly never angry at all. And here is OG Soleum angry at a moments notice.