Not firing on all cilinders.

A can short of a six-pack.
The wheel is still spinning, but the hamster is long dead.
Room temperature IQ.
As sharp as a marble.

Followed this guy while in my bicycle. He had music blaring. When I stopped next to him at the traffic light, we exchanged a glance. The look on his face explained the text on the back of his scootmobile: no cilinders firing in the top floor. We greeted and I complimented him on his choice of music. Then our way parted...