Do people ever get a vitamin overdose?

Yes: You can definitely overdose on fat-soluble vitamins (vitamins a, d, e, and k), because the body stores them in fat, and too much of them can cause an excessive buildup in your body. Water-soluble vitamins (b vitamins and vitamin c) are generally very difficult to overdose, because your body just eliminates what it doesn't need. Can get side effects though, such as kidney stones from too much c.