If there is one thing that I genuinely dislike it will definitely be interrupting my class whether by knocking on the door or any other means 
Last week a student knocked the door once, twice.. over & over. I ignored her completely. She opened the door @ her body language implied that she was asking for some sort of a favor. I normally allow all late students to join in the class even if it is one minute left. So I kept on delivering the lecture. She proceeded to me, I carried on lecturing and waved to her to sit down. She grabbed the closest seat. I went back lecturing. With every move she made to talk, I just kept on lecturing. Towards the end of the lecture, the class got so quite watching a youtube vid, so did I. She came over, knelt down and said: “Miss, I’m not a student of yours, but someone is asking for you.”
Zainab Alqublan's Workspace 