What is this?

What is this, and does it come off by just taking the nut off?

 

Starting to think they wanted to install a ground terminal in plastic.
Yeah I know there's a red wire there but there's also one that goes to ground.

 

Ambient temp sensor? Running out of guesses...

 

The wiring diagram shows an "open air temperature sensor". That's got to be it.

 

Well, whatever it is was added by the PO when he installed HIDs. The parts fiche shows just a plastic rivet. I was going to replace the HIDs with stock headlights but I can't make sense of what he did. Does anybody recognize it as a fastener?
I keep digging, trying to understand what I'm seeing but it's going to need a separate post.

 

I have seen small LED lights that use a similar fixing as shown, maybe your bike had some snazzy underbody lighting? You are correct that the parts in question normally just have one of those small plastic push clips.