Part of a
folksy-sounding
insult, "not exactly the sharpest
tool in the
shed", which means "not very
smart". It's the sort of thing
Foghorn Leghorn would say.
Of course, not all tools need to be particularly sharp. A sledgehammer may not exactly be the sharpest tool in the shed, but it's still damn useful. Fortunately, we've got all kinds of tools in the Everything shed.