Dark Souls. When, after falling through the floor four times, killing a boos in a breeze because it got stuck on some gravel and couldn't turn around to attack, and not getting to save that bennie either because I fell through the floor for a fifth time, getting stuck in the wall a couple times, getting knocked into a part of the dungeon you're not supposed to be able to go to, and so being unable to move at all, but the enemies couldn't attack me either because of invisible walls. After all that, I was going up in an open-walled elevator, and it got stuck and was juddering around like it was on the end of a tiny rubber-band, not going anywhere. In fact, I first thought it was an earthquake, but it just kept going on and on, and I soon realized the game had borked again. So, I went to suicide off the side of the elevator, and discovered that there was an invisible wall protecting you from falling off. That moment.