Go to youtube and start a video...any video. Once the ad (if any) is over, type 1980. Don't type it into search, just enter it on your keyboard.

haha, I love missile Command

Hehe, pretty nice. I remember another one a little earlier where it would turn every comment in the comment's section into 1337 speech. It was both funny and annoying.

Edit: It still works if you write "1337" on your keyboard.