So the reason habitual drinkers can drink so much without effect or much of a hangover is that they've developed tolerance. They make a lot of the enzyme called alcohol dehydrogenase that breaks down alcohol. Since their body habitually is flooded with alcohol, the enzyme is almost constantly made. But if you don't use it, you lose it so if you don't habitually drink, your body doesn't make it, alcohol accumulates and you get what amounts to a poisoning--vomiting, dizziness, slurred speech and a headache of a hangover in the morning.
I have to be careful with red wine--Californian give me a headache. Most champagne too. And hard liquor gives me a really bad hangover, not worth it.