And stop with this "internal values," "logical reasoning," "Fi," "Ti" crap. For one thing, you can't type functions based solely on observed behavior, especially not in a fictional character. That's backwards. And for another, The Joker used a lot of logical reasoning in, for instance, the speech he gave to Harvey Dent and his encounters with Batman. What he didn't do, and indeed did the exact opposite of, is imply that he had any internal values that he made decisions based on. Moreover, what he really desperately wanted most was for people to make sense, and their values, morals and feelings made no sense to him. And, again, MOST IMPORTANTLY, there is absolutely no way the Joker would score as an F on an MBTI test. Never.