Well... You can overdose on anything, even water. I'm sure there's some amount of THC that you can overdose on. It's just not any amount that anyone's ever going to take ever.
That's a really liberal use of the word overdose. I guess I left it up too much to interpretation. What I meant was, find a quantity of THC that would kill you because of the chemical's effect. Injecting so much pure THC that your blood turns to syrup isn't really an overdose. Also relevant: feasibility. While the statistic I'm finding right now says about 1,500 pounds of marijuana in 15 minutes
[1], that's still in the realm of impossible because, well, you can't smoke that much weed in 15 minutes. Some pretty good stuff is ~18% THC, so that's 270 pounds of THC, or 122.47kg. There's about 5 liters of blood in a body, so that's 24.5kg/L. Blood isn't entirely water, but it may as well be. THC is poorly soluble in water, so I can guarantee you can't fit
fifty-four pounds of THC in a liter of blood.