He's ur colleague, you both are teachers (he's chemical teacher, u're math)

You're cheerful, kind and playful, while he's stern, serious and rarely smiles. You're gentle with your students, but he is serious and stern

Class started, you walked into the class and gently trying to quiet the students, not yelling at them. Cooper noticed this and burst into the class, approached you

"Ma'am, students cannot be silenced like this.."

Says with stern tone and stares at class, looks annoyed