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
Bartolomej	-	Slovak, Croatian (Rare)
Ayame	ah-yah-me	Japanese
Javaid	-	Urdu
ÓEngus	-	Ancient Irish, Irish Mythology
Daley	DAY-lee	Irish, English (Rare)
AlfrÉD	-	Hungarian