Someone who is "all there" in a mental sense but not necessarily in a physical one.
Steven Hawking is totally screwed on man.
dari Simon Batt Rabu, 12 Januari 2005
Opposite to someone who has a screw loose i.e a bit dopey.
You obviously had your head screwed on while you were tackling that piece of coursework.
dari Simon Batt Kamis, 13 Januari 2005