Disclaimer: Although I sometimes would like to own a Death Note, the anime and the manga are not mine and although I possess a copy of the game Psychonauts, that too isn't mine.
Author's note: This so had to be written...I don't know where I read it, but somewhere the question was brought up why Matt wears goggles, obviously my mind jumped to that conclusion, especially with him being so fond of video games.
The Purpose of the Goggles
Every time someone asked him why he was wearing goggles all the time, Matt simply smiled at them lazily and shrugged, before returning to his current video game. One day however Mello found out why, not by asking, but by trying to kill him (not in earnest, but then again, you could never be sure with Mello).
"You bastard! You weren't supposed to see that!" he yelled at Matt, who was laughing hard at the sight before him and this only fuelled Mello's rage. "If you tell anyone what you saw, I am so going to scratch out your eyes!" he threatened. "No, even better, I fucking kill you and then I plug out your eyes." At first he thought he succeeded, because Matt stopped laughing, but then his friend grinned cockily at him.
He adjusted his goggles over his eyes and said: "Ha! You can't," his grin widened even more. "THAT is the purpose of the goggles."
Mello didn't get the joke, although he was fairly sure there was one, but he didn't care too much as he leaped at Matt to throttle him. Matt wouldn't stop grinning, however.
He had waited very long to use that specific quote.
Author's note: Even I don't know what Matt saw, so I leave that to your own more or less naughty imagination. As always: be aware that English is not my native language and any constructive criticism is highly appreciated.