is when 20 four colour pens inserted up someones ass one by one and then pulling then all out at once with black shit on them. Them you put them in your mouth and eat all the shit of them.
An idiom, generally used when referring to teachers, describes when a person looks extremely mad at someone else or yourself, and they (in their head) "click a pen", ready to write someone up, or explode on the offender later.
Did you see the wayMr. Rogers was looking at me? He totally just clicked a pen in his head.