I doodle. But only when I am bored, and/or forced to be somewhere I don't want to be (meetings! bad presentations at conferences!).
My doodles usually end up being some kind of picture (various flowers, suns, etc.) and when I was a grad student, and subjected to a particularly aweful, boriing, tedious, teacher, who continously referenced the same critic (who was probably 100 years old!), I would draw caricatures of her, one with her being stabbed, hung and shot by various teachers, with the critic hobbling through the door, beard down to the floor and supported by a cane, coming to help her, and arriving too late (being subjected to another person's incompetence really brings out my nasty side!).