My interpretation of Johnny (spoilers)
Some of the stuff I'm about to write is not original but I feel the need to express my thoughts en toto on this film.
Johnny is the ultimate nihlist. He's bent on self destruction during the peiod in which this film takes place for reasons that are not specifically clear but I don't think specifics matter. Somebody said it's becasue his mother sexually abused him but, even if that's the case, it's incidental.
I think one of the most important moments in the film is when Johhny denies that he is bored. This is obviously a lie. He's way smarter, at least intellectually, than every other character in the film. The only way that he can be entertained by people around him is to indulge his dark side to the fullest and just totally screw with everybody he comes across. His screwing is merciless and extreme, indicitave of extreme boredom.
He abuses Louise by denying her the one thing she wants which is to connect with him. He never really answers any of her questions throughout the whole film. He abuses Sophie by making her fall in love with him and we know where that goes. He abuses Brian in two ways. One by finding out what makes Brian sleep well at night (the whole future/destiny thing) and intellectually ripping that to pieces and the second by disrupting the fantasy that Brian has about the woman across the way. His abuse of the woman across the way is interesting because it's mainly to mess with Brian but, while he's at it, he might as well pull her hair steal her favorite book. She's in too much of a drunken stupor to be a really entertaining target anyway. He abuses The Cafe girl by illustrating how dull she is and then adds insult to injury by guit tripping her when she reacts to it (I think there's more here but I don't see it yet). He abuses the sign poster by just generally disrupting the guy's very apparent focus in doing his job. He abuses Sandra just by messing with her uptightness but eh seems to emphathize with her exsaperation.
I find it interesting that the only characters he does not abuse are the Scottish couple. I think this is because they are so tragic on thier own that he just wants to spectate at thier insanity. They're the only characters he shows curiousity in. He seems very disappointed when they just run off at the end of that sequence.
His encounter with Jeremy is not quite clear to me. It's the only character he tries to legitmately bond with. I'm guessing it has to do with him recognizing the pure evil in Jeremy and his natural attaction to the prochecy of self destruction. Jeremy seems to embody the emotional darkness inside him that he is actualizing throughout the film.
Another detail that I think is important is that he hints that he is very ill in some way. He says something to Brian about it but I couldn't quite figure out what he said. That combined with his apocalypse beliefs, I beleive, are the impotus for his self destructive ways.
Thanks, if you read all that.