I can't perfectly describe what happens but I'll try — the page jumps around with a cat image, every time I try to kill it with cmd+w, it repawns into another small window. I think it remaps cmd+w to cmd+p, and just plays dubstep in the background. Oh, and at some point, a random cat headbanging cat appears, and the voices goes from saying "a-a-a-a-a-a-a-a-a" to "I can't see the inside of my mouth".
I think it also logged me out of gmail.
I had to kill Chrome. Don't open it in your main browser, use incognito mode, or the private browsing mode of a different browser so that you can kill the entire browser without losing HN access — because that's what you'll probably end up doing.
Edit: Oh, it seems to be easier to kill on Firefox. Also, it keeps asking for webcam and mic access, and to be set as the default application for bitcoin links?!!!
Edit: A way to get out without killing Chrome is: "press cmd+w" to get to the "print" screen. That seems to stop the windows from moving around. Then kill all the other windows first, and kill this "print" window last. You'll it say "please don't go" every time — but don't give in!