I'm going to cheat and say that the worst thing we (male/female/other) are told is to be something other than our best selves. Whether we are told to dominate, be dominated, suppress our talents, nature, or expression, feign interests or force gendered skill acquisition, feel shame or pride, or avoid certain types of friendships with certain people, we are being confronted by a system of control. To me, it is the most detestable thing, because while biology can be especially frustrating in its own right, norms are a society's own doing. Society's role is artificial, and its underlying problems can't be fixed with hormones and surgery.