TSGO.
…the use of Olympic Material transformed into graphic animated formats such as animated GIFs (i.e. GIFV), GFY, WebM, or short video formats such as Vines and others, is expressly prohibited.
The reason? The official rights holder is NBC, and the IOC is protecting them by not allowing news agencies to share GIFs that might keep you from watching the actual broadcast on television. Why watch the actual event if you can see the highlights—both hilarious and impressive—in GIF form on your Twitter feed?