I’m terribly sorry if this post offends you, but I do feel like using this word, 害人. Know this is a slang and includes exclusive discrimination so badly. 害[gai] means harm, damage, and 人[jin] means a person. Did you get it? 害人 naturally means a person who does harm to everybody else literally, so in short, it simply means a trouble or an asshole.
But actually, this pronounciation, gaijin is the same as 外人[gaijin] which means a foreigner. So the truth is, this 害人 means a foreigner who harasses everybody else. I am not sure whether this term was born in 2ch, but I often hear about such a 害人 on the net. Especially, a bulletin borad for language exchange because such 害人 people are looking for a date by using language exchange though there are numerous bulletin boards where they can find love romance or friendship. You know, I have tried to use such a bulletin board to find a language exchange partner since I am seriously learning English. However, almost all of the people who had contacted me, stopped mailing when they knew I am a guy. This makes me very upset. Why do they use language exchange for girlhunting? It really harasses serious learners. As I have said above, when things like this happen, I feel like using this slang, 害人. （｀^´）