I'm talking of course about the lack of explanations given for House's supposed attempt to kill Chase on the episode House Divided.
My first reaction to that scene was "what the hell?!?!". It has never been hinted that House either likes or dislikes Chase any different than any of the other ducklings (old or new), so why on earth would he ever want him dead? I thought it was really lame at the momment, and since I couldn't find a good explanation for it I decided to ignore it and pretend it never happened.
But weeks later, after watching Both Sides Now, I finally found an explanation that not only made sense to me but also fit perfectly and could've been a hint of what was going to come (if you squint :P).
House doesn't do well accepting other people's joy and contentment, he's not the type to be happy for you, he almost seems to find it comforting to know that most people have some degree of misery, probably because then his even bigger misery isn't so out of place, would mean it's practically a human condition to have a bit of misery, he might be more miserable than the majority of the people but not by much.
So I'm guessing that the news of Cameron and Chase's wedding made him feel a little resentful, made part of his deep subconcious to wish them appart.
Now, on the episode Both Sides Now the patient suffered from a condition which separated the right side of his brain from the left one, which led him to have two completely different thought processes even though he was only aware of one, the other one was kept in his subconcious. Without the two sides of his brain being able to interact the guy had no control over his actions, the rational part of his brain couldn't control the irrational part of it, like any normal person's brain does.
This caused the patient to become irrationally angry at his girlfriend for little things and even hit her. The girlfriend thought that his act of violence towards her meant he had hidden feelings of anger or contempt for her, that he was actually a naturally violent person and it was only now revealed. But she was wrong, the fact that his rational mind can't control his irrational mind means the poor guy is out of his mind, none of his actions were his fault.
Let me explain it better. Imagine you are walking down the street, listening music on your iPod, pleasantly lost in your thoughts. Suddenly, a guy bumps abruptaly but accidently into you, makes you fall over, drop your bag full of papers, it's a big mess. You glare at the guy and think to yourself "DIE! DIE! DIE!".
Now that's your irrational mind talking, the right side of your brain that controls emotions wants to get up and beat up the guy for ruining your perfect peacefulness. But the left side of your brian, the rational one, knows that it was an accident, that nothing good can come from punching the guy, so the rational mind allows the irrational mind to, at most, yell at the guy to watch where he's walking, that is the worst way in which a normal person would react. And it is better this way because the irrational mind is too caught up with the feelings of the momment to make the right decision, if you follow your irrational mind and beat up the guy, afterwards if the guy is really injured the irrational mind itself will feel guilt for hurting a guy who unintentionally annoyed you. That's why we let the left brain take control in these situations.
But a person who's out of their mind, who doesn't have the left side of the brain to control all irrational impulses, will most probably act on those enraged thoughts and attack the guy.
Back to House, he's hallucinating, we can hardly consider that to mean he is on his right mind, and apparently hallucination-Amber represents the right side of his brain, the irrational one. So House hears the news about Chase and Cameron's wedding and feels some resentment for it. With his brain not working the way it is supposed to, hallucination-Amber suggests to get Karamel for the bachelor party, already knowing how she did the shots and already knowing about Chase's alergy. This is clearly his irrational mind acting, part of it feels the need to break Chase and Cameron appart, and with House being out of his mind, irrational brain works behind rational brain's back to get what it wants. Just like the example of the guy bumping into us on the steet, House's irrationality overreacted, acted on it's own and it resulted on him trying to kill Chase.
Like I explained before, sometimes the right brain itself overreacts and does things it will regret later, our irrationality can't plan ahead, can't think of consequences. I don't think House only felt resentment over Chase and Cameron getting a 'happily ever after', it was just his irrational first reaction, there's another part of him that mentally gave the 'ok' to it. The proof of this part is in the scene of Both Sides Now where he gives Cameron the advice that makes her go back to Chase, the "would you go homeless?" momment. Why would he help her make this decision if he hated Chase and really wanted the relationship to fail? There were mixed feelings in him about their marriage, but I think at the end he decided to accept it.
House trying to kill Chase was a sign of how out of his mind he was falling, it kept getting worse until he actually got to the point where he could hardly separate reality from hallucination. Good thing he went to the psych hospital before he actually killed someone.