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.'