I was able to look at an unfamiliar problem outside of my expertise and spent a a few minutes really working to solve it ,instead of passing it off as outside my field. And those five minutes worked (followed by a month of review and mulling, followed by hours of number crunching, we created a viable solution), now I'm a more experienced, more valuable professional working for a firm with a larger market share.
As in Joshua Blaine's original description (below), but may be used to brag about things you've accomplished either this month (January) or the previous one (December), assuming that you haven't brought it up in any earlier Monthly Bragging Thread.