Consider the tip jar, that common feature of the cafe counter. Unlike the standard 15-percent tip for a waiter, there is no rule of thumb that applies to tip jars. And, unlike restaurant service, there is much less information on which to base the gratuity. You order, you pay, you receive change, and then, often before you even get served, the tip jar beckons. So, in the absence of a rule of thumb, we propose the following: no politeness, no tip. Admittedly, this is a low standard. Yet, it is striking how often one encounters a worker in the tip-jar economy who conducts the entire transaction with barely a word or glance. It takes little effort to smile, offer a greeting and provide a word of thanks. If your server has mastered these basics of customer service, you may want to consider a modest tip. Otherwise, ignore the tip jar in defense of good manners.