A small minded person stuck in a small town. To have zero Insight or enlightened perspective. To be completely self absorbed to the point of blindly engaging with losers dipshits.
A reference to Sherlock Holmes, the main character in a series of mysteries by Sir Arthur Conan Doyle. The detective often solved cases by noting miniscule evidence. The phrase is often used sarcastically when someone points out the obvious. However, it can also be used seriously when someone solves a mystery.
"Dude, The sky is blue today!"
"Way to pull a Sherlock, man!"
"So i figured out where all my towels were going. I found three in Ashleys' dryer. Apparently she has the same ones."
"Way to pull a Sherlock."