The folks at http://www.indiefilmreview.com/dewdeath.html have come up with a handy Dew Death Calculator to let you know how many 12 oz. cans of The Green Death you'd have to chug to overdose on caffeine.

To save you the effort, a table:
  • 100 pounds = 124 cans
  • 150 pounds = 149 cans
  • 175 pounds = 215 cans
  • 200 pounds = 248 cans
The lethal amount is known as the LD50, the amount it would take for 50 percent of the subjects in the sample to keel over dead. In other words, you give a hundred 200-pound people all the Mountain Dew they want, and 50 of them will die after chugging 248 cans. Thus, the LD50 (short for lethal dose).

Actually, the above table is a big fat pack of lies. If you could even drink that much liquid, the water would burst your organs and the sugar would put you in a Sunny Von Bulow-like state long before the caffeine poisoned you. Salud!