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Used when describing a person who is not all there mentally, that is inept socially etc, or appears to be a bit thick. Struggles to fit into normal society, and subsequently rejected and described to people as a bit slow.
May also be used lightheartedly if someone is perhaps day-dreaming and not paying attention when asked a question. Similar to, but not quite the same"a few beers short of a six-pack", or "a few screws loose."
What if we asked Dudley if he knows?
What? You're kidding me right? Theres no way he'd know. In fact stay away from that bloke
Why's that?
You know, The lights are on but nobody is home.
Oh, ok thanks for the warning.

I can't remember, hang on a sec, i'll ask Harold.
Harold, whats the price of that Xbox again, you know the one you bought from E-bay?
I said, how much was that X-box you got from E-bay the other day?
Oh? umm, ahh, hang on a sec
Sorry for the hold up Mavis, old harold here is in another world, the lights are on but nobody's at home, heheh.
by jamie_ledge July 19, 2006
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