Dwight tries to logically reason his relationship with Jim: Jim is Dwight's enemy, but Jim is also his own worst enemy. Therefore the enemy of Dwight's enemy is his friend. So Jim is actually Dwight's friend. But Jim is also his own worst enemy, and the enemy of a friend is an enemy. So Jim is...what? It is fallacy in humor because though the logic makes some sense, it goes in circles and puts Dwight in the same spot but more confused than helped.