Aggressive techniques within casual sex encounters, such as taking sexual liberties without permission or ignoring rejection, can, perhaps unintentionally, complicate consent. Passive recipients may acquiesce out of fear, which aggressors may not realize. Some philosophers argue that social norms are sufficiently well known to make this misunderstanding unlikely. However, the chance of aggression leading to non-consensual sex, even if not great, is high enough that aggressors should work diligently to avoid this potentially grave result. I consider how this problem plays (...) out in the common mating ritual of hooking up. I argue that aggressive hook ups can only be permissible if they are modeled on BDSM encounters: the participants must obtain prior consent and prepare safe words for voiding that consent during the hook up. While this solution removes the spontaneity of aggressive sex, I argue that spontaneously aggressive hook ups with strangers cannot be permissible. (shrink)