Jiff,
Congratulations on the 5K!

You've established your
PR (Personal Record); now your next task is to beat it! You may not remember me, but I started running 5K races just a year ago. I'll tell you what the "Look" means. They are thinking, "Good for you, Girl! You are out here DOING IT!" I am quite famous for being in charge of bringing up the rear guard, and one thing I say is that I beat all of those people who were afraid to show up! I received a beautiful trophy yesterday for being third in my age group for the year in the local runners' club.
I know there are a lot of buff runners out there, but there are also a lot of us particularly in the 5K races that are there to be healthy and do the best we can. It is true that walkers are a problem for runners - I can't tell you how many times I've had trouble getting past four or five walkers walking abreast next to each other who lined up at the starting line rather than paying attention and starting towards the back of the pack with the walkers and slower runners like me. But they are most likely beginners, so I pick myself up when I fall trying to get around them and just keep on going! The whole point is to keep going.
And I am thrilled by every walker who shows up for a 5K - maybe they will get the bug! You'll know when you have the 5K bug when you plan your weekend around the next race!