How much caffeine is actually too much?
Individuals vary too much on their absorption of caffeine to give hard and fast numbers as a reply, but there are a few indicators that you should look for when nearing your own limits to caffeine intake.
If that incessant staccato drumming you hear isn't actually the three year old next door trying to tear through the apartment wall, you might want to check your heart rate. And if everyone around you is mysteriously walking and talking in slow motion, while anxiously examining you, you might want to cut back a little.
Well known examples of over-stimulation through caffeine include Miss Eugenia Krebs, who was found simultaneously painting her toenails, typing out the contents of the her Master's thesis (while not actually being in graduate school), and vacuuming her cat. On the bright side she wound up with one dandy entry to grad school, but her cat left her.
And there is the case of Gerald McRaney, a prolific gamer, who after ingesting 12 Red Bulls in succession went outside for a smoke, and became fascinated with the songs in the night. Turns out he was listening to the echo location signals of the local bat population.