Uni as in "uniformed officer." It's a term used for a beat cop if I recall correctly. I hear it used a lot on "Castle" coming from Ryan, Esposito or Beckett.
Oh. I'm waiting for Netflix Instant list to bring that one back so I can finally see what all the hype is about.
It would be evily hilarious to see the shock on the guy's face if they saw him at a crime scene (maybe "Wall of Sound"?) only to have Henderson tag the guy on the shoulder and give him a look that says "can it."

I agree.