You could start with the mind games, have him come in on the weekend, sundays usually piss people off more than saturdays. Then when he gets there tell him that you actually finished up the work that needed to be done, and sorry for the inconvenience
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But the simplest way to get anyone to quit is to mess with their money. You could cut back his hours, send him home early every other day, or simply decrease his pay.
Of course have a meeting with him first if you're going to permanently cut his hours or decrease his pay, just to prevent lawsuits.
