After coming out to Applejack, Rainbow tells the farm mare that since the Sisterhooves Social, Big Mac had become a target of the homophobes in Ponyville.

Having been their previous target, Dash had defended him in every instance she witnessed. But Applejack wonders if it hurt him more than it seemed -- after all, she couldn't even tell something was up until she was directly told. So, she sets out to get to the bottom of it.