Smashed my thermometer into 80-degree (i.e. ready to pitch) imperial stout. Set me back $40 on ingredients, $15 on a new (non-glass) thermo, and a load of pride. 
So my wife bought me a mr beer kit which catapulted me into homebrewing. I took the 2.5 gallon container and concocted a horrendous extract brew which i thought would be great. Pitched the yeast at 10 pm and by 6 am i had an extremely active fermentation. I put so many fermentables and yeast into the container that mr beer fermenter would not sit flat on the counter on account of the pressure. In a fit of panic in my kitchen i turned the lid about 1/4 turn and the top shot off like a cannon and splattered my kitchen ceiling with hops and other chunks. That was about 6 months ago and to this day that container sits in my basement (wort and all) as a reminder to think about what the hell im doing