Explanation of this pic, please...

[rs232]

So what's the go with the blue, er, ... thing ... ?

 

[kuel]

it appears to be an extra lapel button hole my good man

 

[dopey]

The tab looks derivative of a throat latch tab, cut to allow the coat to button at the throat (this one appears to not be cut correctly and won't work, but that is hard to tell). Note that it is a keyhole buttonhole (meant to button) unlike the lapel buttonhole, which is not.
The fact that thread is bright blue is to signal that the wearer is an idiot, by drawing attention to the fact that the wearer is an idiot.

 

[Zenny]

Its meant to be a buttonhole to fasten to a button under the right lapel, incase coverage is needed for the upper chest.

The fact it is blue is just for sake of ostentatiousness.

 

[ohm]

I believe the purpose of the blue stitching is to bring out the color of the wearer's eyes.

 

[element02]

Do you know who made this jacket? Is there a full picture? Please correct me if I'm wrong, but the tab suggests it's a hacking jacket.

 

[RyanM]

Originally Posted by rs232

So what's the go with the blue, er, ... thing ... ?

Don't worry about it, you're not advanced enough to know the secrets of blue lapel button holes.