Vitamin C is an important antioxidant that humans, along with the rest of the great apes, and some other less relevant animals like guinea pigs, bats etc., have lost the ability to synthesize. We lost this ability at a time when we were largely frugivorous and were thus ingesting plenty of it.
Along the way, we've lost uricase, which is an enzyme that breaks down uric acid, another antioxidant. It's tempting to therefore dismiss the importance of vitamin C and rely on the RDA or whatever amount doesn't produce obvious symptoms of scurvy. Well avast, ye swabs, we should be ingesting a lot more of it.
The Hadza are a group of hunter-gatherers who reside in Tanzania. Hominins have been evolving there since we broke off from our shared ancestor with chimps and bonobos about 7 million years ago. Groups of hunter-gatherers in this region have been exploiting largely the same species of plants and animals for millions of years. As such, it is my contention that the Hadza are the single most important hunter-gatherer group for the study of optimal human nutrition. I believe that all hominin populations outside of the tropics are on marginal lands and though there have been adaptations to these conditions, the vast majority of our genetic code has been selected with the conditions under which the Hadza live "in mind." Just as 2 million > 10,000, 7 million > 60,000. I can think of no population less relevant to the study of worldwide optimal human health than the Inuit, whereas the Hadza have a far greater chance of being broadly applicable.
The Hadza diet is comprised primarily of baobab, tubers, flesh and seasonal berries, with as much honey as they can find. Baobab is the single largest contributor of kcals in their diet and is a surprisingly rich source of vitamin C. There is a variable amount of vitamin C content in the fruit that depends on the tree, but I have seen the range listed as 1500 to 5000 mg/kg. Given that they eat so much of it, daily gram dosages are not out of the realm of possibility. The baobab pods are available almost year-round since the trees produce pods at different times. The Hadza move their camps fairly regularly, but almost always have a source of this important food.
Though a person of northern European descent may be better at coping with reduced intake of vitamin C compared to a Hadza, I think it's safe to say that there is a significant evolutionary precedent for quite high vitamin C intakes and that those who pursue gram dosages every day are not the wackjobs they're made out to be here and elsewhere. Vitamin C is one of the least toxic (and cheap) supplements you can buy. I've never seen any evidence that supplementing with gram doses is harmful, only insistence that it's not necessary. Because many here avoid fruit for God knows what reason, simply taking a supplement should suffice, though I suspect that there are various other compounds not yet fully understood that are in foods like baobab that are also beneficial and that we have evolved alongside.
I therefore recommend that pure ascorbic acid be purchased and dosed 1/8th tsp (500mg) at a time (mixed with plenty of water) several times a day. Those wishing to not amplify their iron absorption (and/or diminish their copper and zinc absorption) would do well not to take it with meat, organs, shellfish etc. Similarly, because the structure of vitamin C is so similar to glucose, they share absorptive mechanisms. As such, it would be best not to take it with starch, since the glucose would be in far greater amounts and drown it out, as it were. Thus, it seems to me that taking it on an empty stomach 15-20 minutes before meals may be optimal, and that bowel disturbances should not occur at this dosage, provided that it is sufficiently diluted.
Edit: Dragonfly brings up the important consideration that ascorbic acid, as you might imagine, is highly acidic and would be best not to have it contact your teeth. I always swish water after taking vitamin C (or eating any fruit or starch for that matter) but forgot to mention that.