[learc83]

"but killing yourself with pot would be pretty tough, and expensive"

It seems to be impossible to actually overdose from the THC contained in marijuana. No one has actually managed to kill a large mammal with THC, but they have managed to kill small rodents.

Extrapolating up it seems that you might be able to obtain a lethal dose of THC by consuming somewhere between 1/3 of your body weight and 1500 lbs of marijuana (all at once).