What if he was subjected to psychological torture, specifically obsenely lurid visions sent to him by Voldemort through whatever the hell connects their minds together? Like being forced to watch Death Eaters rape their way through an all-girls Catholic Boarding School, or something similar. That would probably push almost anyone over the edge, if they were in Harry's place.

 

No it would just make him guilty most likely, he seems to blame everything that happens where Voldemort is involved on himself.

No I believe that under the right circumstances he would snap.

1.Sleep depravation

2.Constant pain i.e his scar

3.And horrible guilt

This provides us with a very flammable mixture, all you need to do is light the match and watch the house go up in flames.

 

Which is increadibly idiotic; because how the hell is it in any way, shape, or form his fault what a psychotic mass-murderer does? God, just who are we talking about here, Harry Potter or Shinji Ikari?

 

If you look at his various outbursts, they do get worse as he gets older. Look at the pattern:
1) Aunt Marge - Accidental magic, blows her up
2) Malfoy insulting his mother - physically beating him up
3) Sirius' death - Cruciatus Curse on Bellatrix (once only)
4) Dumbledore's Death - Multiple Cruciatus Curses on Snape.
5) Ron/Hermione/Ginslut's Death? - Killing Curse on ???.

To make him totally snap you'd have to pile some more pressure on him, possibly have Remus die - last link to his parents gone, have one or two of his friends tortured in front of him, their capture being his fault and then have one of his closest friends die to save him. Probably Ron, as the chess match in book 1 indicates. I think he'd go off the deep end at that point, probably killing curse then mutilating the body or going on a killing spree.

Fun Fun Fun.

Aekiel

 

We do see Harry getting very emotional from the memories brought on by Snape's legilmancy of his mind, it seems to me that with his way of coping with loss (angsting a bit and then ignoring it) is one of the things that keeps him going. If that is removed and he is constantly reminded of bad things that he considers 'his fault' as well as suffering attacks and visions from Voldemort there is the possibility of him snapping.

How this would be achieved I don't know but psychological torture seems to me to be the only way of breaking him and it would need to be constant. We see repeatedly through the books that if Harry has time to regroup then he is the ultimate survivor, both in physical and emotional damage.