Thick as a . . .

Can somebody help me with the word thick-head...

Thanks in advance.

Ex:
if you're too thick-headed to understand that >>OR<< to grow your hair back, then I'm better off without you!

Thick-Headed = Stubborn

Unless you're in the UK, where it means stupid.

It means stupid in the US as well. Mule-headed would be stubborn.

Renowned worldwide for our subtlety and sensitivity, we Irish use 'Thick as a ditch' and 'Thick as two planks sideways' so as not to offend anyone.

Hmmmmmmmm.......I stand/sit corrected!
I checked m-w and thickheaded means lacking in intelligence, blockheaded, dense, doltish, dumb, hebetudinous,obtuse,stupid,thick-witted.
Hebetudinous?