This happened a few years ago now, at the 1997 World Athletics Championships in Athens, but I don't think it's been posted before. Nebiat Habtemariam, an Eritrean long-distance runner, was competing in the 5000 metres and had to borrow someone else's vest due to a kit shortage. The vest was way too big so her boobs kept popping out for the full 18 minutes of the race. The shots are not high res but still tell the story pretty well - in several you can see the poor girl grappling with her top trying to cover herself up - must have been the longest 18 minutes of her life