Giphy is a Chrome extension which helps you find animated GIFs for Gmail, Twitter and HipChat.
When you're composing a message, click the "Search in a Giphy" button and a panel appears with various animated GIFs. If you see one you like, drag and drop it into the message window and you're done.
You'll probably want something more specific, and clicking the menu icon bottom left displays some suggested themes: "Applause", "Awesome", "Eye Roll", "Face Palm", "Goodbye" and many more. Clicking the one you need displays a range of matching GIFs and you just choose your favourite.
If that doesn't work, there's also a search box where you can type in whatever keywords you like.
The extension only works with a few sites, but if you want to use a GIF elsewhere then right-clicking it displays the usual options to copy its URL or save the file locally.
Search in a Giphy is a fun way to find and use more animated GIFs.