The milk thing is because your body can't process the lactose in milk fast enough... so as kidan said you don't have enough stomach/throat to hold it all
Water will process alot quicker but it probably depends how big you are to see if you can down a gallon in a short period of time.
Que, Intoxication (from alcohol) is dehydration.. hence the hangover the next day, so you're right it probably is very similiar.
Lion: Milk is the opposite of acid. Its a base. You drink enough of it, it neutralizes your stomach acids and then you puke from the food in your tummy just sitting there.