The word "pinhead" is used to describe someone who is not very intelligent or clever. It is often used to criticize someone's lack of knowledge or understanding about something. Full definition
For the current batch I threw some into a cooked pot of pinhead oats and ate little bowls of it all week with toasted walnuts, maple syrup and half and half. (101cookbooks.com)
As for these voices of disturbing angels on pinheads as if ancient poetic guardians of some Platonic dance it is over as these distractions are frivolous annoying sideshows. (dotearth.blogs.nytimes.com)
In my 30 years as a professional actor, being cast as Pinhead in HELLRAISER: JUDGMENT is hands - down the coolest thing that... (bloody-disgusting.com)