Slow on the uptake...

[Marsh]

�not the sharpest tool in the box��.one slice short of a sandwich�� 

What's your favourite phrase for this unfortunate condition?

[EssJay1]

The lights are on, but no-one's home...
Not the brightest button...
They're no Einstein...
Ah...bless. But he DOES try...

[spudqueen]

One sandwich short of a picnic

[Grunty]

The wheel is turning, but the hamster has died.

[Skids]

The engine's on but no-one's driving.
Six cans short of a four-pack.

[andy hughes]

Hasn't got both oars in the water. The lift doesn't reach the top floor.

[Chillum]

one tentacle short of an octupus.

[calleach]

lights on nobody home

[Philtaz]

He's got a flash-to-bang time of 30 seconds.

As thick as a workhouse butty.

[Dark Angel]

Not very clever...

[graemer]

One chop short of a barbeque.

He's got kangaroos loose in the top paddock.

[jno]

thick as pigsh*t - though this lacks the wit and subtlety Marsh may well have been looking for in his/her question

[Xollob]

Thick as two short plankton.

[Xollob]

Intellectual gastropod.

[ursula62]

At college we used to say "if your brain was made of cork it wouldn't make a bathmat for a microbe".

[delboy3]

Two clowns short of a circus

[delboy3]

If brains were dynamite you wouldn't have enough to blow your hat off

[kick3m0n]

I love Grunty's phrase...LOL!

[amarillis]

Few beers short of a six pack

Few peas short of a casserole

If he had another brain it would be lonely

[smudge]

I agree kick - I laughed my head off at Grunty's!

[magicdice]

the sharpest spoon in the drawer