I tried that once. I was late to class and grabbed a half gallon to drink Postworkout. Then I thought I would drink one everyday. I gained a lot of bodyfat, and I felt miserable most of my summer. I've always had a hard time gaining weight, so it was easier for me to get kcals in by drinking them and I have an insatiable love for milk. Was it stupid? Probably. Did I gain pure muscle from it? No. But damn, I love milk. I don't regret my decisions.