One of my worst is:

I was cooking dinner for 100 people, in a kitchen that I had never used before. Everything was going fine until I got to my egg and onion pies. I turned the oven on and waited for it to warm up. I placed a oven Thermometer in the oven. It seemed to be running hot so I turned it down and placed the pies inside. Seven minutes later, the pies were completely carbonized and the Thermometer had shattered. needless to say I was not a happy camper.