The act of tapping stationary (most commonly pens or pencils) on the edge of a table or book to emulate the rhythm of a song played on one's ipod or in one's head. This inevitably has the effect of irritating everyone around the pencil drummer and causing him/her to be hit around the head with a textbook, salmon or any other heavy object to hand.
Often accompanied by terrible, unaccompanied singing on the part of the drummer.
Person 1: 'dum da ba dum da ba dum da ba-'
Person 1: 'Fuck dude, what was that for?'
Person 2: 'Quit pencil drumming. Douche.'
The act of pretending to be drummer by tapping 2 pencils on a desk or other hard surface, usually much to the annoyance to those around said pecil drummer.
Look at that guy over there pencil drumming, it annoys me so much. See also Air Drumming and Air Guitar.