The most important point has been missed - are we talking about death from acute toxicity or death from cardiac and/or respiratory distress? See, with a methamphetamine "overdose" the victim usually dies from - in the simplest term - a heart attack .. now this could happen to you after a tiny line - if you have some sort of heart problem then you're taking a risk introducing ANY AMOUNT of meth into your system...
As for death from acute toxicity... damn, I would say more meth then you could pack into your beak in one sitting... you would probably stop from the drip and the meth running down yer throat before you could cook yourself....
But this is really a Health question, so I qill move it there...