I wasn't able to include a link but it is easily found on YT. It's on his "Live from the Beacon Theater" live show. The hairjob reference is at the end of the performance. Around the 55:00 mark.

It's a bit about constant perverted thoughts. He says instead of being a normal guy and doing something like going to a library he says his thoughts instead are about the librarian and wanting to wrap her hair around his dick and jerk off!

It is too funny. Louis CK is the man!