A measuring device that every man has to measure the length of his penis. Could be a ruler, a yardstick, or something else with a predetermined size. Rarely seen or admitted to, but in the possession of most men.
In nominal terms, a dickstick is another term for a dildo. By extrapolation, "dickstick" is a Tomism (see Tomism) and used as a mild insult to one's intelligence. Useable as a substitute for "dipshit", "dickstick" usually indicates one's displeasure of another person's actions.