The spiciest food I've ever had was at Ruen Pair (Thai) in Albany, CA. I have been to many Thai restaurants where I asked for SPICY, or EXTRA SPICY and they just wimp out, and think all whiteboys are total pussies. Ruen Pair asks you "do you know how our spicy is?" and I decided to try it. It was near convulsion-inducing spicy, but the flavor of the chile was delicious. (The other dishes were medium, which were spicier than most places when I ask for SPICY, and were just about perfect.) The next day was just "on fire" unpleasant in the departure department.

What has become my favorite Thai place (Sabuy Sabuy II in Berkeley) will make it about as spicy as above if you ask and make it clear that is how you want it.