Generally accepted as not only one of the most complex and twisted love affairs in comics, but also one of the longest romances between two supervillains, the Joker and Harley Quinn's relationship has been characterised by trauma and abuse of almost every description. With Harley inevitably in a submissive role, the relationship could be used in Health classes in high schools to educate teenagers on the dangers of domestic abuse. Historically an incredibly abusive relationship, the pair's love affair eventually culminated in a killing spree of the Joker's former henchmen, with Harley unaware that her own death would form the eventual "punch line" of the massacre. Apparently love can survive many things, but attempted murder isn't one of them. Harley survived by shooting the Joker in the shoulder, and the pair haven't been together since. The relationship between the Joker and Harley Quinn made this list just because of the high level of psychological, emotional, and physical abuse. There's also the question of how the relationship began. Dr Harleen Quinzel first appeared in the 90's Batman Animated Series as a psychiatrist working at Arkham Asylum. While treating the Joker, Harleen quickly became fascinated with the madman, and eventually freed him. So, to recap, Harley started out as the Joker's psychiatrist before becoming his girlfriend, breaking him out of a secure mental institute, and embarking on a crime spree. And they say romance is dead.