I didn't use my a torque wrench for the crank bolts when I but a new crank set on my fixed gear. It also seems I didn't torque the chainring bolts enough. A couple weeks into the new set up I noticed my chainring was loose, while I was at school.

"F my stupidity" I said, and quickly pulled out my chainring bolt tool and tightened them down(yes I carry one with me). On the way home my non drive side crank falls off! Luckily I was only two miles from home so I managed to ride with one leg. I still had to go to the LBS for a new bolt though. It's a good thing I have clipless pedals or else that thing would have been thrown into the street and run over.

The minute I got home I busted out the torque wrench. I don't know what I was thinking when I tried to get those crank bolts tight with a little 6 inch hex key.