Someone who is either an idiot, or spends too much time taking drugs. Someone who shows signs of minimal intelligence and/or common sense.

This phrase can be used in an offensive or a friendly context.
"Look at that prick, he's fuckin tuned to the moon, so he is"

"Ah've goat my giro, ah'm gonna be well tuned tae the moon the night so ah am"
by Scott T The Silver fox January 23, 2004