No one has ever overdosed on Vitamin C. That said there are distinct reasons to stick to recommended doses of the stuff. You might be stocking up on cheap vitamins and hoping to curtail that oncoming cold by shoving a whole pile of them in your mouth but most likely these will simply be flushed out of your system very quickly. A clear sign that you have gorged on more than your share of Vitamin C is in the brightness (in both yellow and even occasionally nearly orange) of your urine.
There are other potentially pitfalls of forcing large amounts of cheap vitamins packed with Vitamin C down your throat that have little to do with the hue of your pee. These pitfalls include things like insomnia, diarrhea, nausea, vomiting, abdominal cramps, head ache and eventually in extreme cases kidney stones. Obviously these things are all at varying degrees rather unpleasant conditions to have to stomach. What is perhaps more important for those attempting to use the extra vitamins to fight their cold or fever is that with all of that Vitamin C just spilling right back out of you, you’re doing absolutely nothing to get any healthier any quicker.