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
Malcom	['mælkəm]
Guiscard	gees-KAHR	Medieval French
Moshe	-	Hebrew, Biblical Hebrew
Cailean	KA-len	Scottish
Prokopy	prah-KO-pee	Russian
Lorne	LAWRN	English