What is the most cramped Commerical Airplane in use today?

I am still facing the shakes from my last experience fighting closterphobia from three hours in a completely full CRJ Regional Jet. While I was sitting on the flight and walking back to the restroom I was wondering if it was in fact squeezing more people per square inch than any other Airplane. While I know there is many more passengers in a full Boeing 747, there is also more space per passenger.

What Commerical Airplane squeezes the most people per square inch?