What are kidney stones? How about maybe the most painfull experience you will ever have. They are usually either protein or calcium in composition, but unless you're genetically disposed, they only form under the rarest of conditions.
I had a very very small kidney stone once upon a time after I got very dehydrated and had been habitually drinking iced tea. (not a good idea... the oxalates sometimes contribute to kidney stones. there is a general correlation between kidney stones, and what is labeled as the 'iced tea belt' in the US). I rushed myself to the hospital in agonizing pain, only for the stone to break up before it was ever passed. Most people have nothing to worry about, even if they're drinking a lot of milk. The best advice is to stay well hydrated.