When students lose focus completely
I never thought Armin was dumb. He may not be the most brilliant person, but he seems pretty normal to me XDD And you're right, I haven't noticed he worries about reminding people that he isn't stupid or something. As you mentioned, it does look like it bothers him. Do you think it's possible that Armin was bullied before? Now I want to headcanon that Armin had dyslexia when he was younger and the other kids bullied him for having learning disabilities. I would relate to him so much more!