Teacher entered the class little Jonny

When the teacher entered the class little Jonny slowly said:

“Sir excuse me; your zipper is open.”

So the teacher thanked him and fastened his zipper.

He went near little Jonny and told him:

“My dear it would better to say: the office door is open.”

The next day when the teacher entered the class, unfortunately, his zipper was again open!

Little Jonny loudly shouted:

“Not only the office door is open but also the teacher is at the door and two small students are beside him.”