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
Konstantinos	kon-stahn-DEE-nos	Greek
Jannah	JAN-ə	English (Rare)
Dhaval	-	Indian, Marathi, Gujarati
Petre	PE-tre (Romanian)	Romanian, Macedonian, Georgian
Natalia	nah-TAH-lyah (Polish, Italian, Spanish)	Polish, Italian, Spanish, Romanian, Georgian, Late Roman
Sameera (1)	-	Arabic