1) Over-tightened the steerer tube bolt, ripping the threading out of the star nut.
2) Got my laces caught while riding my T1... not really mechanical, but still FML
3) My friend asked me to retension his rear wheel. No bike stand (I was at his house) so I just flipped it upside down. After retensioning, he asked me to degrease and clean his chain. At that moment I was checking the tension of the chain... seeing if I could pull it off. I was so shocked by his request that I turned around to the left, in doing so, my right hand went to the right, and was sucked between the cog and chain (since his bike was upside down). Ended up breaking my finger and cracking two nails.