Milk will generally stay good for over 24hrs unrefrigerated, remember people were drinking milk long before refrigeration, it just helps it last a lot longer. If it were bad you would KNOW it because it would have turned sour. Drinking soured milk will often make you feel ill and even throw up, if it is really bad there could be bacteria in it that could make you sick. But most people can't handle the taste of "rotten" milk and can't drink it anyway.
I can't imagine that it taste very good. Overnight probably isn't going to do anything. The body has a great way of telling us that drinking that was a bad idea, we call it throwing up, tossing our cookies, blowing chunks, letting loose with a pavement pizza, & a host of other fun terms. So bad for you no, if your body tells you differently try & make it to the throne, the oval office etc