Never - no lab animal larger than a rat has ever been successfully killed with THC, and there has never been a well documented case of human THC overdose death.
Look, I already know you reject scientific evidence if it contradicts your narrative that marijuana is perfectly safe.
If there is an LD50 in rats, it is not very different from the LD50 in humans. And do you really think that we are going to test LD50s in humans?
There have been deaths due to THC, and with the increased usage that results from legalization, the death toll will increase. Not that I really care about the deaths; the people who are permanently brain damaged and become permanent (costly) burdens on society due to addiction are a far greater problem.