I hate critical failures. Most campaigns I am in don't have fumbles for skills, it's always just a failure when someone rolls a one.
There was one campaign I was in, 'twas amazing. I was doing well and my party and I were journeying through a forest along the road. We are all asked to do a spot check and we all succeed in noticing the ogre coming down the road towards us. We all decide to hide but end up scrambling off in different directions. It is at this point that I am worried about my character. All the other characters are less melee inclined and more ranged or magic skilled. I unfortunately happen to be the unlucky human fighter wearing full plate, dragging around a glaive and a longbow, and leading around a barded horse. I was the last to get to the treeline to hide and was requested to make both a move silently check and a hide check. I am panicking at this point. I roll two low numbers and smack myself in the face because of the results. At this point I am sure the party expected me to be attacked, but luck for me, the Ogre rolled two 1's and I escape to hide in the treeline. I am requested to do it again, and the Ogre fails yet again. I am happy and excited at this point and I smile. Unfortunately, the next check I fail horribly and the Ogre notices me. The Ogre rushes forward and slams his tree sized club into me, succeeding with a critical hit and sending me flying. My party rushes out, initiative is rolled and combat follows. I proceed to stand up and pull out my weapon on my first turn. The second turn comes around and I attempt to slice the Ogre with my Gliave. At this point I am determined to kill this thing. I roll my dice to determine if I hit and roll a one. My Glaive goes flying behind me and gets stuck in the tree. My turn ends and everyone continues the round. I am once again hit by the Ogre and am suffering from internal injuries. My turn rolls around once more. I draw my bow, knock my arrow, and pull the string back. I roll to hit and once again roll a one. As I am pulling my bowstring back it snaps and my arrow falls to the ground. On the following turn the Ogre manages to get my down to 1 or 2 health and pin me under a tree trunk before succumbing to the combined forces of my allies.
I was DMing a campaign and one of my players was playing a human fighter with custom Dwarven Rock Armor. All the players started in a dungeon performing tests for the Lich headmaster of the college they were trying to enter. All was going well until they entered the room with all the traps. A player walks into the room and ends up succeeding at dodging the pitfall trap, the human fighter was not so lucky. He wanders over another pitfall trap and fails his reflex save. He ends up falling and taking enough damage to drop him to 3 health. Everyone is freaking out and trying to get the human fighter out of the pit. A small rescue operation is formed and the player begin to devise a way to get him out of the trap. They lower a rope in to get him out. As they are doing this, the player decides that he wants to undo the armor around his crotch and proceed with toughing himself. He ends up crushing his part in his giant rock covered hand, dealing 3 damage to himself and moving him into the dying state, the rolls agreeing with him and not I.