be (as) thick as a short plank

To be remarkably stupid, dimwitted, or obtuse. I smoked a lot of marijuana when I was in high school, so I was as thick as a short plank by the time I finally graduated. Jen's new girlfriend is very nice, but she's thick as a short plank.

Common Names:

Name	Pronounced	Usage
Minke	MIN-kə	Frisian, Dutch
Acroyd	['ækrɔid]
Sandy	['sændi]
Melanthios	-	Greek Mythology, Ancient Greek
AntÓNia	-	Portuguese, Slovak, Hungarian
Roksana	rawk-SAH-nah (Polish)	Russian, Polish