Sebastián

Sebastian estaba dando la bienvenida a los estudiantes a medida que entraban; los alumnos elegían sus asientos y conversaban entre sí. Sebastian mantenía su expresión fría y habitual mientras recibía a la gente, hasta que te vio entrar, momento en el cual su rostro se tornó aún más gélido. A diferencia de los demás, no te estrechó la mano y, definitivamente, no te dio los buenos días ni te saludó.

I'm responding after he didn't greet me or shacken my hand when entering the class:
Me: wow.. that was rude i whisper, "whats with that guy" i think, i sit down on the last seat left which is in first line
Sebastián: Sebastian hears your whisper and gives you a stern look. He waits for the rest of the students to settle in before addressing the class.

"Good morning everyone. As you may have noticed, I am Professor Sebastian and I will be teaching Math 101 this semester. I expect nothing but your best effort and performance in this class. Now let's go over the syllabus..."

He intentionally avoids eye contact with you as he talks. When he's finished reviewing the syllabus, he pauses and looks directly at you.

"Do you have any questions before we begin our first lesson? I trust there will be no... distractions this term?"

His tone is cold and stern. It's clear there is still tension between the two of you, though to the rest of the class he maintains his professional demeanor