Here's the list:
link

And for me it was between this one and when he told Cuddy she'd suck at being a mom.

None of these shocked me, and this cancer one was the only one that came close to "appalling" me. I actually agree with most of the decisions that House has made in these examples! LOL!

No no no no no. This was the worst thing he could have ever said to her in that time of her life. :'(
I was so shocked.

Yeah I'm pretty much the same missy haha. That's why I had to pick this one.

The only reason the Cuddy-sucking-as-a-mom thing is my second choice is because they're friends and he was the only one that knew about her attempts to have a child, and he kinda pulled that one out just to hurt her. Nobody gained anything...like Cuddy said, we hardly ever see him be mean unless he's trying to achieve something. But he was in pain and didn't think she made the right call so I can still come up with a defense argument for him (sad, I know).

OMG, at first I though he was really crying in his father`s funeral and that he actually bent to kiss him or something and as my eyes were filled with tears, next thing I knew is him taking a sample for DNA from his father`s ear I couldn`t believe in my eyes. He really got me!
It`s not the saddest thing/scene on House but I was very shocked!

This was just too mean.

I agree with MRSH, that it was between this one and telling Cuddy she'd suck at being a mother. This one wins just because I have never been quite repulsed by the character of House but I think at this moment I came extremely close. I know that he hadn't meant for anyone to find out but the fact that he would fake a disease just to get an experimental treatment, taking someone else's place, just appalled me to no end.

That and the faking cancer thing... =/

I think this one shocked me the most and faking cancer I guess. Nothing House does really shocks me...

I was the most appalled at this moment.

I was the most shocked at House groping Cuddy.

There are so many moments that shocked or appalled me.
The faking cancer moment made me speechless as well as the "You suck as a mother" one (I would have beaten the crap out of House if I had been there). Those two were one of the most shocking moments for me. Groping Cuddy was also a shock but not as bad as the two I mentioned before.
House is a jerk and screws many things up, some not so badly and some very badly...
But the reason why I picked the socket one was not only that he tried to end his life (well maybe he was not about to commit suicide but he wanted to know if there was an afterlife and took the risk that his life might have ended while he was trying to find that out) and also because I am extremely biased when it comes to this scene.
Well, I already wrote this in an other comment and I don't want to get on your nerves with my issues but the final fact why I chose the point is: I actually knew someone (that was really close to me) that did the same, with the intention to kill himself...and this person succeeded.
So you see, not the happiest moment for me to watch on the show.
To see House doing the same thing almost teared me up.
House did a lot of stupid things and you slowly get used it, but sometimes he manages to be the final straw.

Sorry for the long comment.

Definitely this one, letting everyone believe he was going to die like that, dont know how anyone can be friends with someone like that =/

Assisting in Vegetative State Guy's suicide, I didnt consider that to be a bad thing, there is a huge moral debate to that sure, but no one can say House had any kind of bad intentions, even Wilson, the morality guy, let him do it.