Once managed to blow up a monitor.
We used to have a machine where it wouldn't power off automatically, so you had to press the off button after it had shut down.
The next PC we had turned off after shutting down, and then the monitor would power down shortly after. In an automaton state, I ended up pressing the PC's button just after it turned off. Somehow, I magically managed to time it so the monitor tried to turn on and off at the same time. Apparently it didn't like it, and went bang. Think it got replaced under warranty lol.
Edit: Remembered other things I've killed. Killed the obligatory number of earphone wires (yay) and a mobile - a Nokia 3310. I killed it by hitting it against a wall (I was having stress issues, and phone being a pain and dropping calls wasn't helping), and managed to dislodge the mic/wiring in it, and then noone could hear me on calls lol.
Current phone holding on strong so far... bounces off walls too

(Samsung E250 iirc). Not thrown it in a long time tho.