A friend of mine drank grain alcohol straight one weekend and he said he had a horrible sore throat for a 3 days.

Alcohol is hydrophilic. It pulls water out of the air, your skin, and your mucus membranes better than the driest air. This is also how it kills bacteria - by dehydration. When you drink Everclear straight, some of the alcohol remains in your throat after you swallow and is subsequently inhaled where it dehydrates the cells lining the trachea. The cells die and you get a sore throat.