How do you erase certain parts of the memory?

[MulleDK19]

...of course, that's assuming even a hypnotist would have the power to do that.

I highly doubt a hypnotist would have that kind of power at all--no one can just snap your fingers and make you forget like that. The only things I can see that would make you forget are the following:

1.) Getting hit in the back of the head hard/repeatedly.
2.) Coming down with a condition that, in some fashion, deteriorates brain function (i.e. Alzheimers)
3.) Having so much stress/trauma associated with that kind of memory that you end up actually suppressing it. And I mean a LOT of stress--like, you'd have to be close to completely losing your sanity. A hypnotist, at this stage, might be able to help you forget. Not to mention that it would be...odd if you really encountered such high levels of stress over a video game.

There could be others I'm not thinking of at the moment though.

I'm a hypnotist, and I've got no trouble making anyone forget, lol.