There was a page in the early 2000s called the most annoying website in the world. It showed a very large (but finite: the site itself estimates 30-45 minutes) number of alerts. It also a prompt for your name and referred to you by your name.
At the time I knew only HTML so I was blown away by a web page "talking" to me, and by inspecting the source I learned about the script tag, alerts, prompts, loops and variables.
When it came out, the main browser was Internet Explorer, which became unresponsive until you got rid of all of the alerts. You could of course use Task Manager, or hold spacebar to go through them quickly, but most people didn't know that.
Edit: holy smokes it's still up!