This is very true for water-soluble vitamins of which C is one. You CANNOT overdose on them because the body will naturally eliminate whatever it does not need and you will have diarrhea, at the very worst.
The story is very different for fat-soluble vitamins! Since these are stored in fat, it is possible to do harm with too much of a good thing. Vitamins A & D are two examples...although too much betacarotene will just make you turn a funny orange color!