Muppet juice

Slang for alcohol. Drinking enough of any type makes you move like a Muppet where your arms and legs move oddly and you stare at people strangely while talking to them.

Muppet juice is another word for meth. When meth addicts lose their teeth( and most do) they look like Muppets (puppets made famous by Jim Henson. Such as the Muppets and fragil rock)

Meth being the "juice" that causes this. "Muppet effect"

Muppet juice is the term used to describe liquid methamphetamine that is used for injection purposes. It's often used by people that inject methamphetamine directly into the bloodstream using a hypodermic syringe.

The reason it's called Muppet juice is because not all but many amphetamine users have no teeth due to the amphetamines and lack of care cause their teeth to rot out (meth mouth)
So in essence the methamphetamine has caused them to have no teeth and they look like a muppet. So when they are asking for their drug of choice they refer to it as Muppet juice