Find an animated gif you want to use. Upload it to your photobucket account.
Then go to profile > modify profile > forum settings . Click on specify avatar by URL and enter the URL of the one you want in the box, then hit save.
Well that's easy enough, if you're smart! ^-^
btw, that kitten/slide gif you have is perhaps the cutest thing I've ever seen on the internet!
If I could find one I liked that well, I might change my Tea-Party-DC-event-personal-experience photo I have there now.