I only listen to headphones on the MUP where there is no vehicular traffic. I don't worry about being passed because it almost never happens. I had one of those annoying rollerblader taking up the whole MUP once and she couldn't hear me screaming at her. I had to reach out and touch her flailing arm to get her attention and of course she almost took me out. I also often don't announce when I'm passing people as the general response is for people to look behind them which causes them to veer directly into my path. That or they slow down to the point of feeble-wobble and someday one of them will topple over and take me out. The worst, though, are these tards who walk with dogs on retractable leashes and let them stray all the way to the other side of the path. I would like to beat them about the head and neck.