1. Find a youtube video
2. Open this site:
http://makeagif.com/youtube-to-gif3. Paste video URL
4. Set it to where you want it to start and how long (more than 5 seconds requires you to sign up/register).
5. wait for it to produce
6. when it is finished and you can see it, Right-click gif and click on 'Copy Image URL'
7. On forum go to Profile>Modify Profile>Forum profile and click "specify avatar by url" underneath "personalised picture".
And you are done!