What is the most valuable thing you have destroyed in anger?

Long ago, I once threw a book across my efficiency apartment in a fit of rage and it bounced off a kitchen cabinet and nailed the pipe leading into the water heater and caused it to break, spraying water everywhere. It took me 15 minutes to find the shut-off (it wasn't in my apartment) and it ended up flooding my apartment, waterlogged all my stuff, destroying a toaster and a computer (among many other things). It took multiple days to dry out and probably caused a good deal of water damage to the unit. I ended up fixing it myself and didn't report it to the landlord.

After that, I learned to count to ten.