In the video, he's just been kicked out of class, but stops on his way out to criticize the teacher for not motivating the students, and only giving them boring worksheets to fill out.
Here are some great quotes from the video:
"You want [kids] to get excited for this? You gotta come in here and make them excited. You want a kid to change and start doing better? You gotta touch his freakin' heart."
"When you come in here like you did last time, and make a statement about, 'Oh, this is my paycheck,' indeed it is. But this is my country's future, and my education."