I'm surprised there are no mention of techniques to create enough heat to cause a fire. I suppose that's a bit more than a killer poke. Got any links for a 'flaming' poke?
I'm pretty sure this would cause the PET's monitor to catch fire.
My friends and I (as kids) would dare each other to type this into any SuperPet we saw in a computer shop but thankfully we were all too sensible to give it a go.
Mostly we'd say we were going to and instead type
POKE 32768, 115
which (if I remember correctly) would put a love heart in the top left corner instead.
This just brought me back to HS and doing this on all the computer lab C64's (usually contained 3/4 of the way into some Basic program...) After a few weeks of this, there was a nice note posted to each monitor to kindly refrain from killing the machines...
http://en.wikipedia.org/wiki/Killer_poke