Used often in The Maze Runner, it is a replacment for shithead. Also, it is a good word to use around adults. What you call someone who is stupid or a jerk.
Either liquid niquil or any liquid drink with melatonin, Ashwaganda or other sleeping aids in a liquid form. If warm tea helps you get to sleep that could be sleepy juice too.
I could not sleep so I chugged some sleepy juice and now I'm so tired and sleepy.