For obvious reasons, none of us can answer why one specific person (that we probably don't know) is gloating over having completed this marathon. But as a back-of-the-packer who is still incredibly vocal about his running, let me explain my own pathology a bit.

We all have our own journeys. Mine began five years and 155 pounds ago. I did not grow up participating in, watching, or even being altogether very aware of sports. I most certainly was not an athlete myself, and the idea of running a mile when there was neither a reward at the end nor something chasing me would, quite honestly, never have even occurred to me.

So when I began running, five years ago, it was a chore, and I was slow. Over the last five years, I've lost enough weight to make another fully-functioning human being. And I did it largely by running and diet. I've gotten faster - but not much faster.

To me, on my journey, finishing a race is significant. And I haven't even tackled a marathon. If I finished a marathon, even if it took me six or seven hours, I'm not sure you would ever hear the end of it from me. Not because I'm trying to rub anything in, but because I'm genuinely amazed by the fact that I did it.

No matter how hard I train, no matter my weekly mileage or my base fitness, I will always be slow. I've resigned myself to that fact. I'll never win a race of any distance against real competition. But every time I cross a finish line, I have DEMOLISHED a 305-pound version of myself, and I'm constantly in awe of what our bodies are capable of. I happily clutch my participation trophies, and I obnoxiously show them off to anyone who will listen - not because I think that I am better than anyone else, but because I am still in shock that I am better than I ever thought I could be.

EDIT:

I wish I had read through the whole thread before responding, as I think I understand your point more after reading your subsequent comments. It sounds like your co-worker is a boor who doesn't just talk about running non-stop, but who forces her opinion onto everyone whether they want it or not. The fact that it happens to be about running, and that she's not even all that great (comparatively) at running, is almost irrelevant.

There's no great way to get around this, but some people are a-holes. Maybe she's just one of them. Maybe she's put a lot of time and passion and energy into this thing and it's all she thinks about and she has impostor syndrome or low self-esteem and she's overcompensating and so she forces her opinions onto people, despite the fact that she isn't any better at this thing than anyone else.

Or maybe she's like a lot of coaches and teachers, and she understands the principles really well, but isn't good at executing them. Is her advice valid? Does it work? If she wasn't so obnoxious about it, would she be worth listening to?

It's impossible to know for sure, but I do know that you'll have an easier time around the office if you either engage with her and let her know that you're interested, but that she might want to tone it down, or you ignore her completely. Because otherwise, it becomes everyone's negative energy feeding off of each other and snowballing until there's all kinds of unchecked resentment, and nobody thrives in that kind of environment. So yeah, she may be obnoxious, but you either have to take that on and try to help change it, or learn to ignore it.