What's the hardest song you ever learned to play on guitar?

Hard question, I am not even sure how to answer it myself. Mmm, I'll go with the chord melody guitar in "54 Duncan Terrace", by Allan Holdsworth. I transcribed it by myself, and it took a while before I got all the notes right - some very unusual chords in there. It's not that hard to play it, but it was that hard to figure out the chords.
Listen here - http://www.last.fm/music/Allan+Holds...Duncan+Terrace


Also, the melody to "Got A Match" (Chick Corea), very hard to execute cleanly and with good timing, due to the speed!