Instructive Lost? or Just Irritating?

The latest OTB tournament game left a bitter taste as my opponent, a >1900 rater(FIDE), is one of those arrogant braggartly repellent types who are the epitome of sore losers but who, not surprisingly, make formidable chess players.

Fortunately any lingering 'Off-the-board' animosity was avoided by a small error in the end game; let's see if you can spot it...