What's the hardest game you've played?

http://www.ferryhalim.com/orisinal/g3/bells.htm

This bunny game is addicting, entertaining, MAYBE never ending (who knows =])

But its really frustrating when you fall from up there D:

And the annoying music, just complements perfectly to make this one of my hardest games.

My friend's high score was in the billions, if not higher. I'll see if I can get his screenshots off his old HDD.