Theoretically, I imagine that someone could drink enough, say, decaf coffee to trigger hyponatremia (I only say "decaf" to exclude any effect of caffeine--some Brit did actually kill himself by OD'ing on caffeine just the other day). But plain water would be the easiest to cause this problem since it contains little in the way of electrolytes. I think Gatorade would not because it contains too much of various electrolytes, such as sodium. If you didn't get nauseous and throw up from trying to overdose on Gatorade, then I think you'd actually be facing hy-PER-natremia, rather than hy-PO-natremia.

Some casual runners in marathons have a tendency to fall victim to hyponatremia because they drink too much water during the race because they've always heard to drink often and drink a lot. Over the course of 5+ hours on the course, they can drink much more plain water than they are sweating out. But the common wisdom in sports hydration has become more refined over the years. If you watch elite marathoners, they drink very little during the race even though they are working very, very hard.