On some of my old sites I used to check for whether the document was in an iframe, and go into an infinite loop if it was. The trick is to loop/delay slow enough to not trigger the "script is not responding", but enough to make the browser hellishly unresponsive.

Back in the Flash days I had a cherry bomb I'd put in my code that would crash decompilers in a similar way, if it found _root.stage.parent. It would also phone home first ;)