The lights are on, but nobody's home 

1. Literally, when someone leaves their house and forgets to turn off their lights.
2. Joe Biden

1.
John: hey, let's go across the street and drop in on Bob.
Jim: I don't think he's home right now.
John: but his lights are on
Jim: yeah, but I saw him leave a while ago, he must've forgot to turn off his lights when he left again, he does that a lot.
John: damn, I was really looking forward to having a few beers and some great conversation with him!

2. Joe Biden is literally the definition of 'the lights are on, but nobody's home.' I mean he has a brain, (or wait does he?), I mean at least I think he has a brain, but we never see it used and it doesn't work properly most of the time, he's alive and here physically but mentally he's dead and gone.

The lights are on, but nobody's home by Cornpop was a bad dude July 20, 2022

the lights are on, but there's nobody home 

Someone who is mentally vacant. "Fit in body but sick in mind" as one may have said in an ancient Catholic will.

Q:Why does she just sit in that rocking chair all day?


A:The lights are on, but there's nobody home.

the lights are on, but there's nobody home by Kung-Fu Jesus April 21, 2004