Looks like the crank case breather tube....Or some other kind of vent or tube I'm not entirely sure.
I would let someone else chime in with a bit more experience but that's my thought.
I don't think its anything to worry about if its what I think it is, just make sure it doesn't get snagged on anything.
Your motorcycle probably passed by another motorcycle he liked.
It's the drain tube for the air box, It must be periodically cleaned by taking the plug on the end off and letting it drain.