Eating a lot of garlic can lead to acid reflux or other unpleasant effects of overeating an acidic substance. It isn't so much that eating too much garlic is bad for you, as it is that overeating garlic comes with unpleasant side effects. Anyway, eating too much garlic once shouldn't do you any lasting damage. Overeating garlic all the time probably isn't a great idea, and you might want to speak to a dietitian or other professionally trained person about its long-term effects.