Giphy from ThemeHouse unites XenForo 2 and Giphy the popular library of animated gifs for every occasion. Includes content rating filters and endless fun (endless fun not guaranteed).
All you have to do is use the button provided in the text editor on XenForo. Click on that before viewing either a module or the bottom of the editor. Searching a keyword will allow Giphy to randomly pick a gif using the Giphy API. After doing so, select which GIF fits best before posting your thread.
Looking for Giphy for XenForo 1? You can find it by navigating here.